1
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Eltokhi A, Lundstrom BN, Li J, Zweifel LS, Catterall WA, Gamal El-Din TM. Pathogenic gating pore current conducted by autism-related mutations in the Na V1.2 brain sodium channel. Proc Natl Acad Sci U S A 2024; 121:e2317769121. [PMID: 38564633 PMCID: PMC11009634 DOI: 10.1073/pnas.2317769121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Accepted: 02/26/2024] [Indexed: 04/04/2024] Open
Abstract
Autism spectrum disorder (ASD) is a complex neurodevelopmental condition characterized by social and communication deficits and repetitive behaviors. The genetic heterogeneity of ASD presents a challenge to the development of an effective treatment targeting the underlying molecular defects. ASD gating charge mutations in the KCNQ/KV7 potassium channel cause gating pore currents (Igp) and impair action potential (AP) firing of dopaminergic neurons in brain slices. Here, we investigated ASD gating charge mutations of the voltage-gated SCN2A/NaV1.2 brain sodium channel, which ranked high among the ion channel genes with mutations in individuals with ASD. Our results show that ASD mutations in the gating charges R2 in Domain-II (R853Q), and R1 (R1626Q) and R2 (R1629H) in Domain-IV of NaV1.2 caused Igp in the resting state of ~0.1% of the amplitude of central pore current. The R1626Q mutant also caused significant changes in the voltage dependence of fast inactivation, and the R1629H mutant conducted proton-selective Igp. These potentially pathogenic Igp were exacerbated by the absence of the extracellular Mg2+ and Ca2+. In silico simulation of the effects of these mutations in a conductance-based single-compartment cortical neuron model suggests that the inward Igp reduces the time to peak for the first AP in a train, increases AP rates during a train of stimuli, and reduces the interstimulus interval between consecutive APs, consistent with increased neural excitability and altered input/output relationships. Understanding this common pathophysiological mechanism among different voltage-gated ion channels at the circuit level will give insights into the underlying mechanisms of ASD.
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Affiliation(s)
- Ahmed Eltokhi
- Department of Pharmacology, University of Washington, Seattle, WA98195
| | - Brian Nils Lundstrom
- Department of Neurology in the Division of Epilepsy, Mayo Clinic, Rochester, MN55905
| | - Jin Li
- Department of Pharmacology, University of Washington, Seattle, WA98195
| | - Larry S. Zweifel
- Department of Pharmacology, University of Washington, Seattle, WA98195
- Department of Psychiatry & Behavioral Sciences, University of Washington, Seattle, WA98195
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2
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Yuan Y, Li P, Li J, Zhao Q, Chang Y, He X. Protein lipidation in health and disease: molecular basis, physiological function and pathological implication. Signal Transduct Target Ther 2024; 9:60. [PMID: 38485938 PMCID: PMC10940682 DOI: 10.1038/s41392-024-01759-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 12/31/2023] [Accepted: 01/24/2024] [Indexed: 03/18/2024] Open
Abstract
Posttranslational modifications increase the complexity and functional diversity of proteins in response to complex external stimuli and internal changes. Among these, protein lipidations which refer to lipid attachment to proteins are prominent, which primarily encompassing five types including S-palmitoylation, N-myristoylation, S-prenylation, glycosylphosphatidylinositol (GPI) anchor and cholesterylation. Lipid attachment to proteins plays an essential role in the regulation of protein trafficking, localisation, stability, conformation, interactions and signal transduction by enhancing hydrophobicity. Accumulating evidence from genetic, structural, and biomedical studies has consistently shown that protein lipidation is pivotal in the regulation of broad physiological functions and is inextricably linked to a variety of diseases. Decades of dedicated research have driven the development of a wide range of drugs targeting protein lipidation, and several agents have been developed and tested in preclinical and clinical studies, some of which, such as asciminib and lonafarnib are FDA-approved for therapeutic use, indicating that targeting protein lipidations represents a promising therapeutic strategy. Here, we comprehensively review the known regulatory enzymes and catalytic mechanisms of various protein lipidation types, outline the impact of protein lipidations on physiology and disease, and highlight potential therapeutic targets and clinical research progress, aiming to provide a comprehensive reference for future protein lipidation research.
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Affiliation(s)
- Yuan Yuan
- Department of Gastroenterology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Peiyuan Li
- Department of Gastroenterology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Jianghui Li
- Department of Gastroenterology, Zhongnan Hospital of Wuhan University, Wuhan, China
- Hubei Clinical Center and Key Laboratory of Intestinal and Colorectal Diseases, Wuhan, China
| | - Qiu Zhao
- Department of Gastroenterology, Zhongnan Hospital of Wuhan University, Wuhan, China.
- Hubei Clinical Center and Key Laboratory of Intestinal and Colorectal Diseases, Wuhan, China.
| | - Ying Chang
- Department of Gastroenterology, Zhongnan Hospital of Wuhan University, Wuhan, China.
- Hubei Clinical Center and Key Laboratory of Intestinal and Colorectal Diseases, Wuhan, China.
| | - Xingxing He
- Department of Gastroenterology, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
- Department of Gastroenterology, Zhongnan Hospital of Wuhan University, Wuhan, China.
- Hubei Clinical Center and Key Laboratory of Intestinal and Colorectal Diseases, Wuhan, China.
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3
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Lin Y, Tao E, Champion JP, Corry B. A binding site for phosphoinositides described by multiscale simulations explains their modulation of voltage-gated sodium channels. eLife 2024; 12:RP91218. [PMID: 38465747 DOI: 10.7554/elife.91218] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/12/2024] Open
Abstract
Voltage-gated sodium channels (Naᵥ) are membrane proteins which open to facilitate the inward flux of sodium ions into excitable cells. In response to stimuli, Naᵥ channels transition from the resting, closed state to an open, conductive state, before rapidly inactivating. Dysregulation of this functional cycle due to mutations causes diseases including epilepsy, pain conditions, and cardiac disorders, making Naᵥ channels a significant pharmacological target. Phosphoinositides are important lipid cofactors for ion channel function. The phosphoinositide PI(4,5)P2 decreases Naᵥ1.4 activity by increasing the difficulty of channel opening, accelerating fast inactivation and slowing recovery from fast inactivation. Using multiscale molecular dynamics simulations, we show that PI(4,5)P2 binds stably to inactivated Naᵥ at a conserved site within the DIV S4-S5 linker, which couples the voltage-sensing domain (VSD) to the pore. As the Naᵥ C-terminal domain is proposed to also bind here during recovery from inactivation, we hypothesize that PI(4,5)P2 prolongs inactivation by competitively binding to this site. In atomistic simulations, PI(4,5)P2 reduces the mobility of both the DIV S4-S5 linker and the DIII-IV linker, responsible for fast inactivation, slowing the conformational changes required for the channel to recover to the resting state. We further show that in a resting state Naᵥ model, phosphoinositides bind to VSD gating charges, which may anchor them and impede VSD activation. Our results provide a mechanism by which phosphoinositides alter the voltage dependence of activation and the rate of recovery from inactivation, an important step for the development of novel therapies to treat Naᵥ-related diseases.
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Affiliation(s)
- Yiechang Lin
- Research School of Biology, Australian National University, Canberra, Australia
| | - Elaine Tao
- Research School of Biology, Australian National University, Canberra, Australia
| | - James P Champion
- Research School of Biology, Australian National University, Canberra, Australia
| | - Ben Corry
- Research School of Biology, Australian National University, Canberra, Australia
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4
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Raman IM. The Hodgkin-Huxley-Katz Prize Lecture: A Markov model with permeation-dependent gating that accounts for resurgent current of voltage-gated Na channels. J Physiol 2023; 601:5147-5164. [PMID: 37837315 PMCID: PMC10913027 DOI: 10.1113/jp285166] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Accepted: 09/20/2023] [Indexed: 10/16/2023] Open
Abstract
Many neurons that fire high-frequency action potentials express specialized voltage-gated Na channel complexes that not only conduct transient current upon depolarization, but also pass resurgent current upon repolarization. The resurgent current is associated with recovery of transient current, even at moderately negative potentials where fast inactivation is usually absorbing. The combined results of many experimental studies have led to the hypothesis that resurgent current flows upon repolarization when an endogenous blocking protein that occludes open channels at depolarized potentials is expelled by inwardly permeating Na ions. Additional observations have suggested that the position of the voltage sensor of domain IV regulates the affinity of the channel for the putative blocker. To test the effectiveness of a kinetic scheme incorporating these features, here we develop and justify a Markov model with states grounded in known Na channel conformations. Simulations were designed to investigate whether including a permeation-dependent unblocking rate constant and two open-blocked states, superimposed on conformations and voltage-sensitive movements present in all voltage-gated Na channels, is sufficient to account for the unusual gating of channels with a resurgent component. Optimizing rate constant parameters against a wide range of experimental data from cerebellar Purkinje cells demonstrates that a kinetic scheme for Na channels incorporating the novel aspects of a permeation-dependent unblock, as well as distinct high- and low-affinity blocked states, reproduces all the attributes of experimentally recorded Na currents in a physiologically plausible manner.
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Affiliation(s)
- Indira M Raman
- Department of Neurobiology, Northwestern University, Evanston, IL, USA
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5
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Marques LP, Santos-Miranda A, Joviano-Santos JV, Teixeira-Fonseca JL, Alcântara FDS, Sarmento JO, Roman-Campos D. The fungicide tebuconazole modulates the sodium current of human Na V1.5 channels expressed in HEK293 cells. Food Chem Toxicol 2023; 180:113992. [PMID: 37633639 DOI: 10.1016/j.fct.2023.113992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 08/09/2023] [Accepted: 08/16/2023] [Indexed: 08/28/2023]
Abstract
The fungicide Tebuconazole is a widely used pesticide in agriculture and may cause cardiotoxicity. In our present investigation the effect of Tebuconazole on the sodium current (INa) of human cardiac sodium channels (NaV1.5) was studied using a heterologous expression system and whole-cell patch-clamp techniques. Tebuconazole reduced the amplitude of the peak INa in a concentration- and voltage-dependent manner. At the holding potential of -120 mV the IC50 was estimated at 204.1 ± 34.3 μM, while at -80 mV the IC50 was 0.3 ± 0.1 μM. The effect of the fungicide is more pronounced at more depolarized potentials, indicating a state-dependent interaction. Tebuconazole caused a negative shift in the half-maximal inactivation voltage and delayed recovery from fast inactivation of INa. Also, it enhanced closed-state inactivation, exhibited use-dependent block in a voltage-dependent manner. Furthermore, Tebuconazole reduced the increase in late sodium current induced by the pyrethroid insecticide β-Cyfluthrin. These results suggest that Tebuconazole can interact with NaV1.5 channels and modulate INa. The observed effects may lead to decreased cardiac excitability through reduced INa availability, which could be a new mechanism of cardiotoxicity to be attributed to the fungicide.
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Affiliation(s)
- Leisiane Pereira Marques
- Laboratory of Cardiobiology, Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | - Artur Santos-Miranda
- Department of Physiology and Biophysics, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
| | | | - Jorge Lucas Teixeira-Fonseca
- Laboratory of Cardiobiology, Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | - Fabiana da Silva Alcântara
- Laboratory of Cardiobiology, Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | - Jaqueline Oliveira Sarmento
- Laboratory of Cardiobiology, Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil
| | - Danilo Roman-Campos
- Laboratory of Cardiobiology, Department of Biophysics, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, SP, Brazil.
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6
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Liu Y, Bassetto CAZ, Pinto BI, Bezanilla F. A mechanistic reinterpretation of fast inactivation in voltage-gated Na + channels. Nat Commun 2023; 14:5072. [PMID: 37604801 PMCID: PMC10442390 DOI: 10.1038/s41467-023-40514-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 07/25/2023] [Indexed: 08/23/2023] Open
Abstract
The hinged-lid model was long accepted as the canonical model for fast inactivation in Nav channels. It predicts that the hydrophobic IFM motif acts intracellularly as the gating particle that binds and occludes the pore during fast inactivation. However, the observation in recent high-resolution structures that the bound IFM motif is located far from the pore, contradicts this preconception. Here, we provide a mechanistic reinterpretation of fast inactivation based on structural analysis and ionic/gating current measurements. We demonstrate that in Nav1.4 the final inactivation gate is comprised of two hydrophobic rings at the bottom of S6 helices. These rings function in series and close downstream of IFM binding. Reducing the volume of the sidechain in both rings leads to a partially conductive, leaky inactivated state and decreases the selectivity for Na+ ion. Altogether, we present an alternative molecular framework to describe fast inactivation.
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Affiliation(s)
- Yichen Liu
- Department of Neurobiology, University of Chicago, Chicago, IL, USA
| | - Carlos A Z Bassetto
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
| | - Bernardo I Pinto
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA.
- Centro Interdisciplinario de Neurociencias de Valparaíso, Valparaíso, Chile.
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7
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Gada KD, Kamuene JM, Chandrashekar A, Kissell RC, Yauch AK, Plant LD. PI(4,5)P2 regulates the gating of NaV1.4 channels. J Gen Physiol 2023; 155:e202213255. [PMID: 37043561 PMCID: PMC10103707 DOI: 10.1085/jgp.202213255] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 02/22/2023] [Accepted: 03/22/2023] [Indexed: 04/14/2023] Open
Abstract
Voltage-gated sodium (NaV) channels are densely expressed in most excitable cells and activate in response to depolarization, causing a rapid influx of Na+ ions that initiates the action potential. The voltage-dependent activation of NaV channels is followed almost instantaneously by fast inactivation, setting the refractory period of excitable tissues. The gating cycle of NaV channels is subject to tight regulation, with perturbations leading to a range of pathophysiological states. The gating properties of most ion channels are regulated by the membrane phospholipid, phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2). However, it is not known whether PI(4,5)P2 modulates the activity of NaV channels. Here, we utilize optogenetics to activate specific, membrane-associated phosphoinositide (PI)-phosphatases that dephosphorylate PI(4,5)P2 while simultaneously recording NaV1.4 channel currents. We show that dephosphorylating PI(4,5)P2 left-shifts the voltage-dependent gating of NaV1.4 to more hyperpolarized membrane potentials, augments the late current that persists after fast inactivation, and speeds the rate at which channels recover from fast inactivation. These effects are opposed by exogenous diC8PI(4,5)P2. We provide evidence that PI(4,5)P2 is a negative regulator that tunes the gating behavior of NaV1.4 channels.
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Affiliation(s)
- Kirin D. Gada
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Jordie M. Kamuene
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Aishwarya Chandrashekar
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - R. Charles Kissell
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Anne K. Yauch
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Leigh D. Plant
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
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8
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Liu Y, Bassetto CAZ, Pinto BI, Bezanilla F. A Mechanistic Reinterpretation of Fast Inactivation in Voltage-Gated Na + Channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.27.538555. [PMID: 37162849 PMCID: PMC10168311 DOI: 10.1101/2023.04.27.538555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Fast Inactivation in voltage-gated Na + channels plays essential roles in numerous physiological functions. The canonical hinged-lid model has long predicted that a hydrophobic motif in the DIII-DIV linker (IFM) acts as the gating particle that occludes the permeation pathway during fast inactivation. However, the fact that the IFM motif is located far from the pore in recent high-resolution structures of Nav + channels contradicts this status quo model. The precise molecular determinants of fast inactivation gate once again, become an open question. Here, we provide a mechanistic reinterpretation of fast inactivation based on ionic and gating current data. In Nav1.4 the actual inactivation gate is comprised of two hydrophobic rings at the bottom of S6. These function in series and closing once the IFM motif binds. Reducing the volume of the sidechain in both rings led to a partially conductive inactivated state. Our experiments also point to a previously overlooked coupling pathway between the bottom of S6 and the selectivity filter.
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Affiliation(s)
- Yichen Liu
- Department of Neurobiology, University of Chicago, Chicago, IL, USA
| | - Carlos A Z Bassetto
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
| | - Bernardo I Pinto
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL, USA
- Centro Interdisciplinario de Neurociencias de Valparaiso, Valparaiso, Chile
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9
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Guidelli R. A historical biophysical dogma vs. an understanding of the structure and function of voltage-gated tetrameric ion channels. A review. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:184046. [PMID: 36096197 DOI: 10.1016/j.bbamem.2022.184046] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/18/2022] [Accepted: 09/06/2022] [Indexed: 06/15/2023]
Abstract
The outstanding work of several eminent biophysicists has allowed the functional features of voltage-gated tetrameric ion channels to be disclosed using ingenious and sophisticated electrophysiological techniques. However, the kinetics and mechanism underlying these functions have been heavily conditioned by an arbitrary interpretation of the groundbreaking results obtained by Hodgkin and Huxley (HH) in their investigation of sodium and potassium currents using the voltage clamp technique. Thus, the heavy parametrization of their results was considered to indicate that any proposed sequence of closed states terminates with a single open state. This 'dogma' of HH parametrization has influenced the formulation of countless mechanistic models, mainly stochastic, requiring a high number of free parameters and of often unspecified conformational states. This note aims to point out the advantages of a deterministic kinetic model that simulates the main features of tetrameric ion channels using only two free parameters by assuming their stepwise opening accompanied by a progressively increasing cation flow. This model exploits the electrostatic attractive interactions stemming from the charge distribution shared by all tetrameric ion channels, providing a close connection between their structure and function. Quite significantly, a stepwise opening of all ligand-gated tetrameric ion channels, such as glutamate receptors (GluRs), with concomitant ion flow, is nowadays generally accepted, not having been influenced by this dogma. This provides a unified picture of both voltage-gated and ligand-gated tetrameric ion channels.
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Affiliation(s)
- Rolando Guidelli
- Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy.
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10
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Brake N, Mancino AS, Yan Y, Shimomura T, Kubo Y, Khadra A, Bowie D. Closed-state inactivation of cardiac, skeletal, and neuronal sodium channels is isoform specific. J Gen Physiol 2022; 154:213242. [PMID: 35612552 PMCID: PMC9136305 DOI: 10.1085/jgp.202112921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 05/09/2022] [Accepted: 05/12/2022] [Indexed: 01/07/2023] Open
Abstract
Voltage-gated sodium (Nav) channels produce the upstroke of action potentials in excitable tissues throughout the body. The gating of these channels is determined by the asynchronous movements of four voltage-sensing domains (VSDs). Past studies on the skeletal muscle Nav1.4 channel have indicated that VSD-I, -II, and -III are sufficient for pore opening, whereas VSD-IV movement is sufficient for channel inactivation. Here, we studied the cardiac sodium channel, Nav1.5, using charge-neutralizing mutations and voltage-clamp fluorometry. Our results reveal that both VSD-III and -IV are necessary for Nav1.5 inactivation, and that steady-state inactivation can be modulated by all VSDs. We also demonstrate that channel activation is partially determined by VSD-IV movement. Kinetic modeling suggests that these observations can be explained from the cardiac channel's propensity to enter closed-state inactivation (CSI), which is significantly higher than that of other Nav channels. We show that skeletal muscle Nav1.4, cardiac Nav1.5, and neuronal Nav1.6 all have different propensities for CSI and postulate that these differences produce isoform-dependent roles for the four VSDs.
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Affiliation(s)
- Niklas Brake
- Quantitative Life Sciences PhD Program, McGill University, Montreal, Quebec, Canada,Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Adamo S. Mancino
- Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada,Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
| | - Yuhao Yan
- Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada,Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
| | - Takushi Shimomura
- Division of Biophysics and Neurobiology, National Institute for Physiological Sciences, Okazaki, Japan,Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, National Institute for Physiological Sciences, Okazaki, Japan,Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Hayama, Japan
| | - Anmar Khadra
- Department of Physiology, McGill University, Montreal, Quebec, Canada
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada,Correspondence to Derek Bowie:
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11
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Daimi H, Lozano-Velasco E, Aranega A, Franco D. Genomic and Non-Genomic Regulatory Mechanisms of the Cardiac Sodium Channel in Cardiac Arrhythmias. Int J Mol Sci 2022; 23:1381. [PMID: 35163304 PMCID: PMC8835759 DOI: 10.3390/ijms23031381] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 12/30/2021] [Accepted: 01/06/2022] [Indexed: 12/19/2022] Open
Abstract
Nav1.5 is the predominant cardiac sodium channel subtype, encoded by the SCN5A gene, which is involved in the initiation and conduction of action potentials throughout the heart. Along its biosynthesis process, Nav1.5 undergoes strict genomic and non-genomic regulatory and quality control steps that allow only newly synthesized channels to reach their final membrane destination and carry out their electrophysiological role. These regulatory pathways are ensured by distinct interacting proteins that accompany the nascent Nav1.5 protein along with different subcellular organelles. Defects on a large number of these pathways have a tremendous impact on Nav1.5 functionality and are thus intimately linked to cardiac arrhythmias. In the present review, we provide current state-of-the-art information on the molecular events that regulate SCN5A/Nav1.5 and the cardiac channelopathies associated with defects in these pathways.
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Affiliation(s)
- Houria Daimi
- Biochemistry and Molecular Biology Laboratory, Faculty of Pharmacy, University of Monastir, Monastir 5000, Tunisia
| | - Estefanía Lozano-Velasco
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
| | - Amelia Aranega
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
| | - Diego Franco
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
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12
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Ransdell JL, Moreno JD, Bhagavan D, Silva JR, Nerbonne JM. Intrinsic mechanisms in the gating of resurgent Na + currents. eLife 2022; 11:70173. [PMID: 35076394 PMCID: PMC8824471 DOI: 10.7554/elife.70173] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 01/24/2022] [Indexed: 11/13/2022] Open
Abstract
The resurgent component of the voltage-gated sodium current (INaR) is a depolarizing conductance, revealed on membrane hyperpolarizations following brief depolarizing voltage steps, which has been shown to contribute to regulating the firing properties of numerous neuronal cell types throughout the central and peripheral nervous systems. Although mediated by the same voltage-gated sodium (Nav) channels that underlie the transient and persistent Nav current components, the gating mechanisms that contribute to the generation of INaR remain unclear. Here, we characterized Nav currents in mouse cerebellar Purkinje neurons, and used tailored voltage-clamp protocols to define how the voltage and the duration of the initial membrane depolarization affect the amplitudes and kinetics of INaR. Using the acquired voltage-clamp data, we developed a novel Markov kinetic state model with parallel (fast and slow) inactivation pathways and, we show that this model reproduces the properties of the resurgent, as well as the transient and persistent, Nav currents recorded in (mouse) cerebellar Purkinje neurons. Based on the acquired experimental data and the simulations, we propose that resurgent Na+ influx occurs as a result of fast inactivating Nav channels transitioning into an open/conducting state on membrane hyperpolarization, and that the decay of INaR reflects the slow accumulation of recovered/opened Nav channels into a second, alternative and more slowly populated, inactivated state. Additional simulations reveal that extrinsic factors that affect the kinetics of fast or slow Nav channel inactivation and/or impact the relative distribution of Nav channels in the fast- and slow-inactivated states, such as the accessory Navβ4 channel subunit, can modulate the amplitude of INaR.
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Affiliation(s)
- Joseph L Ransdell
- Department of Medicine, Washington University in Saint Louis, Saint Louis, United States
| | - Jonathan D Moreno
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, United States
| | - Druv Bhagavan
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, United States
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, Saint Louis, United States
| | - Jeanne M Nerbonne
- Department of Medicine, Washington University in Saint Louis, Saint Louis, United States
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13
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Ionic channels in nerve membranes, 50 years on. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2022; 169-170:12-20. [PMID: 34856230 PMCID: PMC8977236 DOI: 10.1016/j.pbiomolbio.2021.11.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Accepted: 11/25/2021] [Indexed: 12/19/2022]
Abstract
This retrospective traces the hypothesis of ion channels from an early statement in a 1970 essay in this journal (Hille, B., 1970, Prog. Biophys. Mol. Biol. 21, 1-32) to its realization today in biophysical, molecular, biochemical, and structural terms. The Na+ and K+ channels of the action potential have been isolated, reconstituted, cloned, mutated, and expressed. They are conformationally flexible, multi-pass glycosylated membrane proteins. Refined atomic structures of several conformational states are known. The discoveries over this half century history illustrate the growth of a field from initial ideas to a mature discipline of biology, physiology, and biomedical science.
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14
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Peng S, Chen M, Xiao Z, Xiao X, Luo S, Liang S, Zhou X, Liu Z. A Novel Spider Toxin Inhibits Fast Inactivation of the Na v1.9 Channel by Binding to Domain III and Domain IV Voltage Sensors. Front Pharmacol 2021; 12:778534. [PMID: 34938190 PMCID: PMC8685421 DOI: 10.3389/fphar.2021.778534] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 11/05/2021] [Indexed: 11/13/2022] Open
Abstract
Venomous animals have evolved to produce peptide toxins that modulate the activity of voltage-gated sodium (Nav) channels. These specific modulators are powerful probes for investigating the structural and functional features of Nav channels. Here, we report the isolation and characterization of δ-theraphotoxin-Gr4b (Gr4b), a novel peptide toxin from the venom of the spider Grammostola rosea. Gr4b contains 37-amino acid residues with six cysteines forming three disulfide bonds. Patch-clamp analysis confirmed that Gr4b markedly slows the fast inactivation of Nav1.9 and inhibits the currents of Nav1.4 and Nav1.7, but does not affect Nav1.8. It was also found that Gr4b significantly shifts the steady-state activation and inactivation curves of Nav1.9 to the depolarization direction and increases the window current, which is consistent with the change in the ramp current. Furthermore, analysis of Nav1.9/Nav1.8 chimeric channels revealed that Gr4b preferentially binds to the voltage-sensor of domain III (DIII VSD) and has additional interactions with the DIV VSD. The site-directed mutagenesis analysis indicated that N1139 and L1143 in DIII S3-S4 linker participate in toxin binding. In sum, this study reports a novel spider peptide toxin that may slow the fast inactivation of Nav1.9 by binding to the new neurotoxin receptor site-DIII VSD. Taken together, these findings provide insight into the functional role of the Nav channel DIII VSD in fast inactivation and activation.
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Affiliation(s)
- Shuijiao Peng
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Minzhi Chen
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Zhen Xiao
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Xin Xiao
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Sen Luo
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Songping Liang
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Xi Zhou
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
| | - Zhonghua Liu
- The National and Local Joint Engineering Laboratory of Animal Peptide Drug Development, College of Life Sciences, Hunan Normal University, Changsha, China
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15
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Angsutararux P, Zhu W, Voelker TL, Silva JR. Molecular Pathology of Sodium Channel Beta-Subunit Variants. Front Pharmacol 2021; 12:761275. [PMID: 34867379 PMCID: PMC8640220 DOI: 10.3389/fphar.2021.761275] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 10/28/2021] [Indexed: 12/19/2022] Open
Abstract
The voltage-gated Na+ channel regulates the initiation and propagation of the action potential in excitable cells. The major cardiac isoform NaV1.5, encoded by SCN5A, comprises a monomer with four homologous repeats (I-IV) that each contain a voltage sensing domain (VSD) and pore domain. In native myocytes, NaV1.5 forms a macromolecular complex with NaVβ subunits and other regulatory proteins within the myocyte membrane to maintain normal cardiac function. Disturbance of the NaV complex may manifest as deadly cardiac arrhythmias. Although SCN5A has long been identified as a gene associated with familial atrial fibrillation (AF) and Brugada Syndrome (BrS), other genetic contributors remain poorly understood. Emerging evidence suggests that mutations in the non-covalently interacting NaVβ1 and NaVβ3 are linked to both AF and BrS. Here, we investigated the molecular pathologies of 8 variants in NaVβ1 and NaVβ3. Our results reveal that NaVβ1 and NaVβ3 variants contribute to AF and BrS disease phenotypes by modulating both NaV1.5 expression and gating properties. Most AF-linked variants in the NaVβ1 subunit do not alter the gating kinetics of the sodium channel, but rather modify the channel expression. In contrast, AF-related NaVβ3 variants directly affect channel gating, altering voltage-dependent activation and the time course of recovery from inactivation via the modulation of VSD activation.
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Affiliation(s)
- Paweorn Angsutararux
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States.,Department of Medicine, Brigham and Women's Hospital, Boston, MA, United States
| | - Taylor L Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
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16
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Priest MF, Lee EE, Bezanilla F. Tracking the movement of discrete gating charges in a voltage-gated potassium channel. eLife 2021; 10:58148. [PMID: 34779404 PMCID: PMC8635975 DOI: 10.7554/elife.58148] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 11/08/2021] [Indexed: 01/18/2023] Open
Abstract
Positively charged amino acids respond to membrane potential changes to drive voltage sensor movement in voltage-gated ion channels, but determining the displacements of voltage sensor gating charges has proven difficult. We optically tracked the movement of the two most extracellular charged residues (R1 and R2) in the Shaker potassium channel voltage sensor using a fluorescent positively charged bimane derivative (qBBr) that is strongly quenched by tryptophan. By individually mutating residues to tryptophan within the putative pathway of gating charges, we observed that the charge motion during activation is a rotation and a tilted translation that differs between R1 and R2. Tryptophan-induced quenching of qBBr also indicates that a crucial residue of the hydrophobic plug is linked to the Cole-Moore shift through its interaction with R1. Finally, we show that this approach extends to additional voltage-sensing membrane proteins using the Ciona intestinalis voltage-sensitive phosphatase (CiVSP).
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Affiliation(s)
- Michael F Priest
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Elizabeth El Lee
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Francisco Bezanilla
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States.,Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, United States
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17
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Savalli N, Angelini M, Steccanella F, Wier J, Wu F, Quinonez M, DiFranco M, Neely A, Cannon SC, Olcese R. The distinct role of the four voltage sensors of the skeletal CaV1.1 channel in voltage-dependent activation. J Gen Physiol 2021; 153:212652. [PMID: 34546289 PMCID: PMC8460119 DOI: 10.1085/jgp.202112915] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 08/22/2021] [Indexed: 11/30/2022] Open
Abstract
Initiation of skeletal muscle contraction is triggered by rapid activation of RYR1 channels in response to sarcolemmal depolarization. RYR1 is intracellular and has no voltage-sensing structures, but it is coupled with the voltage-sensing apparatus of CaV1.1 channels to inherit voltage sensitivity. Using an opto-electrophysiological approach, we resolved the excitation-driven molecular events controlling both CaV1.1 and RYR1 activations, reported as fluorescence changes. We discovered that each of the four human CaV1.1 voltage-sensing domains (VSDs) exhibits unique biophysical properties: VSD-I time-dependent properties were similar to ionic current activation kinetics, suggesting a critical role of this voltage sensor in CaV1.1 activation; VSD-II, VSD-III, and VSD-IV displayed faster activation, compatible with kinetics of sarcoplasmic reticulum Ca2+ release. The prominent role of VSD-I in governing CaV1.1 activation was also confirmed using a naturally occurring, charge-neutralizing mutation in VSD-I (R174W). This mutation abolished CaV1.1 current at physiological membrane potentials by impairing VSD-I activation without affecting the other VSDs. Using a structurally relevant allosteric model of CaV activation, which accounted for both time- and voltage-dependent properties of CaV1.1, to predict VSD-pore coupling energies, we found that VSD-I contributed the most energy (~75 meV or ∼3 kT) toward the stabilization of the open states of the channel, with smaller (VSD-IV) or negligible (VSDs II and III) energetic contribution from the other voltage sensors (<25 meV or ∼1 kT). This study settles the longstanding question of how CaV1.1, a slowly activating channel, can trigger RYR1 rapid activation, and reveals a new mechanism for voltage-dependent activation in ion channels, whereby pore opening of human CaV1.1 channels is primarily driven by the activation of one voltage sensor, a mechanism distinct from that of all other voltage-gated channels.
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Affiliation(s)
- Nicoletta Savalli
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Marina Angelini
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Federica Steccanella
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Julian Wier
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Fenfen Wu
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Marbella Quinonez
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Alan Neely
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA.,Centro Interdisciplinario de Neurociencias de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Riccardo Olcese
- Department of Anesthesiology and Perioperative Medicine, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA.,Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
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18
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Voltage sensor movements of Ca V1.1 during an action potential in skeletal muscle fibers. Proc Natl Acad Sci U S A 2021; 118:2026116118. [PMID: 34583989 DOI: 10.1073/pnas.2026116118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/24/2021] [Indexed: 11/18/2022] Open
Abstract
The skeletal muscle L-type Ca2+ channel (CaV1.1) works primarily as a voltage sensor for skeletal muscle action potential (AP)-evoked Ca2+ release. CaV1.1 contains four distinct voltage-sensing domains (VSDs), yet the contribution of each VSD to AP-evoked Ca2+ release remains unknown. To investigate the role of VSDs in excitation-contraction coupling (ECC), we encoded cysteine substitutions on each S4 voltage-sensing segment of CaV1.1, expressed each construct via in vivo gene transfer electroporation, and used in cellulo AP fluorometry to track the movement of each CaV1.1 VSD in skeletal muscle fibers. We first provide electrical measurements of CaV1.1 voltage sensor charge movement in response to an AP waveform. Then we characterize the fluorescently labeled channels' VSD fluorescence signal responses to an AP and compare them with the waveforms of the electrically measured charge movement, the optically measured free myoplasmic Ca2+, and the calculated rate of Ca2+ release from the sarcoplasmic reticulum for an AP, the physiological signal for skeletal muscle fiber activation. A considerable fraction of the fluorescence signal for each VSD occurred after the time of peak Ca2+ release, and even more occurred after the earlier peak of electrically measured charge movement during an AP, and thus could not directly reflect activation of Ca2+ release or charge movement, respectively. However, a sizable fraction of the fluorometric signals for VSDs I, II, and IV, but not VSDIII, overlap the rising phase of charge moved, and even more for Ca2+ release, and thus could be involved in voltage sensor rearrangements or Ca2+ release activation.
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19
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Angsutararux P, Kang PW, Zhu W, Silva JR. Conformations of voltage-sensing domain III differentially define NaV channel closed- and open-state inactivation. J Gen Physiol 2021; 153:212533. [PMID: 34347027 PMCID: PMC8348240 DOI: 10.1085/jgp.202112891] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 07/14/2021] [Indexed: 11/21/2022] Open
Abstract
Voltage-gated Na+ (NaV) channels underlie the initiation and propagation of action potentials (APs). Rapid inactivation after NaV channel opening, known as open-state inactivation, plays a critical role in limiting the AP duration. However, NaV channel inactivation can also occur before opening, namely closed-state inactivation, to tune the cellular excitability. The voltage-sensing domain (VSD) within repeat IV (VSD-IV) of the pseudotetrameric NaV channel α-subunit is known to be a critical regulator of NaV channel inactivation. Yet, the two processes of open- and closed-state inactivation predominate at different voltage ranges and feature distinct kinetics. How inactivation occurs over these different ranges to give rise to the complexity of NaV channel dynamics is unclear. Past functional studies and recent cryo-electron microscopy structures, however, reveal significant inactivation regulation from other NaV channel components. In this Hypothesis paper, we propose that the VSD of NaV repeat III (VSD-III), together with VSD-IV, orchestrates the inactivation-state occupancy of NaV channels by modulating the affinity of the intracellular binding site of the IFMT motif on the III-IV linker. We review and outline substantial evidence that VSD-III activates in two distinct steps, with the intermediate and fully activated conformation regulating closed- and open-state inactivation state occupancy by altering the formation and affinity of the IFMT crevice. A role of VSD-III in determining inactivation-state occupancy and recovery from inactivation suggests a regulatory mechanism for the state-dependent block by small-molecule anti-arrhythmic and anesthetic therapies.
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Affiliation(s)
- Paweorn Angsutararux
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Po Wei Kang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Wandi Zhu
- Department of Medicine, Brigham and Women's Hospital, Boston, MA
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
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20
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Zhu W, Wang W, Angsutararux P, Mellor RL, Isom LL, Nerbonne JM, Silva JR. Modulation of the effects of class Ib antiarrhythmics on cardiac NaV1.5-encoded channels by accessory NaVβ subunits. JCI Insight 2021; 6:e143092. [PMID: 34156986 PMCID: PMC8410097 DOI: 10.1172/jci.insight.143092] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Accepted: 06/17/2021] [Indexed: 01/28/2023] Open
Abstract
Native myocardial voltage-gated sodium (NaV) channels function in macromolecular complexes comprising a pore-forming (α) subunit and multiple accessory proteins. Here, we investigated the impact of accessory NaVβ1 and NaVβ3 subunits on the functional effects of 2 well-known class Ib antiarrhythmics, lidocaine and ranolazine, on the predominant NaV channel α subunit, NaV1.5, expressed in the mammalian heart. We showed that both drugs stabilized the activated conformation of the voltage sensor of domain-III (DIII-VSD) in NaV1.5. In the presence of NaVβ1, the effect of lidocaine on the DIII-VSD was enhanced, whereas the effect of ranolazine was abolished. Mutating the main class Ib drug-binding site, F1760, affected but did not abolish the modulation of drug block by NaVβ1/β3. Recordings from adult mouse ventricular myocytes demonstrated that loss of Scn1b (NaVβ1) differentially affected the potencies of lidocaine and ranolazine. In vivo experiments revealed distinct ECG responses to i.p. injection of ranolazine or lidocaine in WT and Scn1b-null animals, suggesting that NaVβ1 modulated drug responses at the whole-heart level. In the human heart, we found that SCN1B transcript expression was 3 times higher in the atria than ventricles, differences that could, in combination with inherited or acquired cardiovascular disease, dramatically affect patient response to class Ib antiarrhythmic therapies.
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Affiliation(s)
- Wandi Zhu
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.,Department of Medicine, Brigham and Women's Hospital, Boston, Massachusetts, USA
| | - Wei Wang
- Department of Internal Medicine, Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA
| | - Paweorn Angsutararux
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Rebecca L Mellor
- Department of Internal Medicine, Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA
| | - Lori L Isom
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Jeanne M Nerbonne
- Department of Internal Medicine, Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA.,Department of Developmental Biology, Washington University School of Medicine in St. Louis, St. Louis, Missouri, USA
| | - Jonathan R Silva
- Department of Biomedical Engineering, McKelvey School of Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
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21
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Ghovanloo MR, Ruben PC. Cannabidiol and Sodium Channel Pharmacology: General Overview, Mechanism, and Clinical Implications. Neuroscientist 2021; 28:318-334. [PMID: 34027742 PMCID: PMC9344566 DOI: 10.1177/10738584211017009] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated sodium (Nav) channels initiate action potentials in excitable tissues. Altering these channels' function can lead to many pathophysiological conditions. Nav channels are composed of several functional and structural domains that could be targeted pharmacologically as potential therapeutic means against various neurological conditions. Mutations in Nav channels have been suggested to underlie various clinical syndromes in different tissues and in association with conditions ranging from epileptic to muscular problems. Treating those mutations that increase the excitability of Nav channels requires inhibitors that could effectively reduce channel firing. The main non-psychotropic constituent of the cannabis plant, cannabidiol (CBD), has recently gained interest as a viable compound to treat some of the conditions that are associated with Nav malfunctions. In this review, we discuss an overview of Nav channels followed by an in-depth description of the interactions of CBD and Nav channels. We conclude with some clinical implications of CBD use against Nav hyperexcitability based on a series of preclinical studies published to date, with a focus on Nav/CBD interactions.
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Affiliation(s)
- Mohammad-Reza Ghovanloo
- Department of Biomedical Physiology & Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada.,Department of Neurology, Yale University School of Medicine, New Haven, CT, USA.,Center for Neuroscience & Regeneration Research, Yale University, West Haven, CT, USA
| | - Peter C Ruben
- Department of Biomedical Physiology & Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
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22
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Nakajima T, Tamura S, Kurabayashi M, Kaneko Y. Towards Mutation-Specific Precision Medicine in Atypical Clinical Phenotypes of Inherited Arrhythmia Syndromes. Int J Mol Sci 2021; 22:ijms22083930. [PMID: 33920294 PMCID: PMC8069124 DOI: 10.3390/ijms22083930] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Accepted: 04/08/2021] [Indexed: 12/19/2022] Open
Abstract
Most causal genes for inherited arrhythmia syndromes (IASs) encode cardiac ion channel-related proteins. Genotype-phenotype studies and functional analyses of mutant genes, using heterologous expression systems and animal models, have revealed the pathophysiology of IASs and enabled, in part, the establishment of causal gene-specific precision medicine. Additionally, the utilization of induced pluripotent stem cell (iPSC) technology have provided further insights into the pathophysiology of IASs and novel promising therapeutic strategies, especially in long QT syndrome. It is now known that there are atypical clinical phenotypes of IASs associated with specific mutations that have unique electrophysiological properties, which raises a possibility of mutation-specific precision medicine. In particular, patients with Brugada syndrome harboring an SCN5A R1632C mutation exhibit exercise-induced cardiac events, which may be caused by a marked activity-dependent loss of R1632C-Nav1.5 availability due to a marked delay of recovery from inactivation. This suggests that the use of isoproterenol should be avoided. Conversely, the efficacy of β-blocker needs to be examined. Patients harboring a KCND3 V392I mutation exhibit both cardiac (early repolarization syndrome and paroxysmal atrial fibrillation) and cerebral (epilepsy) phenotypes, which may be associated with a unique mixed electrophysiological property of V392I-Kv4.3. Since the epileptic phenotype appears to manifest prior to cardiac events in this mutation carrier, identifying KCND3 mutations in patients with epilepsy and providing optimal therapy will help prevent sudden unexpected death in epilepsy. Further studies using the iPSC technology may provide novel insights into the pathophysiology of atypical clinical phenotypes of IASs and the development of mutation-specific precision medicine.
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23
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Plant LD, Xiong D, Romero J, Dai H, Goldstein SAN. Hypoxia Produces Pro-arrhythmic Late Sodium Current in Cardiac Myocytes by SUMOylation of Na V1.5 Channels. Cell Rep 2021; 30:2225-2236.e4. [PMID: 32075761 PMCID: PMC7054841 DOI: 10.1016/j.celrep.2020.01.025] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 12/03/2019] [Accepted: 01/07/2020] [Indexed: 01/08/2023] Open
Abstract
Acute cardiac hypoxia produces life-threatening elevations in late sodium current (ILATE) in the human heart. Here, we show the underlying mechanism: hypoxia induces rapid SUMOylation of NaV1.5 channels so they reopen when normally inactive, late in the action potential. NaV1.5 is SUMOylated only on lysine 442, and the mutation of that residue, or application of a deSUMOylating enzyme, prevents hypoxic reopenings. The time course of SUMOylation of single channels in response to hypoxia coincides with the increase in ILATE, a reaction that is complete in under 100 s. In human cardiac myocytes derived from pluripotent stem cells, hypoxia-induced ILATE is confirmed to be SUMO-dependent and to produce action potential prolongation, the pro-arrhythmic change observed in patients. The cardiac channel NaV1.5 passes pro-arrhythmic late sodium currents in response to hypoxia. Plant et al. demonstrate the pathophysiological mechanism to be rapid, hypoxia-induced monoSUMOylation of NaV1.5 channels. Blocking SUMOylation of lysine442 prevents hypoxia-induced late currents and attendant prolongation of the action potential in human cardiomyocytes derived from pluripotent stem cells.
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Affiliation(s)
- Leigh D Plant
- Department of Pharmaceutical Sciences, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA.
| | - Dazhi Xiong
- Departments of Pediatrics and Physiology & Biophysics, University of California, Irvine, 1001 Health Sciences Road, Irvine Hall, Irvine, CA 92697, USA
| | - Jesus Romero
- Departments of Pediatrics and Physiology & Biophysics, University of California, Irvine, 1001 Health Sciences Road, Irvine Hall, Irvine, CA 92697, USA
| | - Hui Dai
- Departments of Pediatrics and Physiology & Biophysics, University of California, Irvine, 1001 Health Sciences Road, Irvine Hall, Irvine, CA 92697, USA
| | - Steve A N Goldstein
- Departments of Pediatrics and Physiology & Biophysics, University of California, Irvine, 1001 Health Sciences Road, Irvine Hall, Irvine, CA 92697, USA.
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24
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Rühlmann AH, Körner J, Hausmann R, Bebrivenski N, Neuhof C, Detro-Dassen S, Hautvast P, Benasolo CA, Meents J, Machtens JP, Schmalzing G, Lampert A. Uncoupling sodium channel dimers restores the phenotype of a pain-linked Na v 1.7 channel mutation. Br J Pharmacol 2020; 177:4481-4496. [PMID: 32663327 PMCID: PMC7484505 DOI: 10.1111/bph.15196] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Revised: 06/24/2020] [Accepted: 06/27/2020] [Indexed: 12/11/2022] Open
Abstract
Background and Purpose The voltage‐gated sodium channel Nav1.7 is essential for adequate perception of painful stimuli. Mutations in the encoding gene, SCN9A, cause various pain syndromes in humans. The hNav1.7/A1632E channel mutant causes symptoms of erythromelalgia and paroxysmal extreme pain disorder (PEPD), and its main gating change is a strongly enhanced persistent current. On the basis of recently published 3D structures of voltage‐gated sodium channels, we investigated how the inactivation particle binds to the channel, how this mechanism is altered by the hNav1.7/A1632E mutation, and how dimerization modifies function of the pain‐linked mutation. Experimental Approach We applied atomistic molecular simulations to demonstrate the effect of the mutation on channel fast inactivation. Native PAGE was used to demonstrate channel dimerization, and electrophysiological measurements in HEK cells and Xenopus laevis oocytes were used to analyze the links between functional channel dimerization and impairment of fast inactivation by the hNav1.7/A1632E mutation. Key Results Enhanced persistent current through hNav1.7/A1632E channels was caused by impaired binding of the inactivation particle, which inhibits proper functioning of the recently proposed allosteric fast inactivation mechanism. hNav1.7 channels form dimers and the disease‐associated persistent current through hNav1.7/A1632E channels depends on their functional dimerization status: Expression of the synthetic peptide difopein, a 14‐3‐3 inhibitor known to functionally uncouple dimers, decreased hNav1.7/A1632E channel‐induced persistent currents. Conclusion and Implications Functional uncoupling of mutant hNav1.7/A1632E channel dimers restored their defective allosteric fast inactivation mechanism. Our findings support the concept of sodium channel dimerization and reveal its potential relevance for human pain syndromes.
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Affiliation(s)
- Annika H Rühlmann
- Institute of Physiology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Jannis Körner
- Institute of Physiology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany.,Department of Anaesthesiology, Medical Faculty, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Ralf Hausmann
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Nikolay Bebrivenski
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Christian Neuhof
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Silvia Detro-Dassen
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Petra Hautvast
- Institute of Physiology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Carène A Benasolo
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany.,Forschungszentrum Jülich, Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Jülich, Germany
| | - Jannis Meents
- Institute of Physiology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Jan-Philipp Machtens
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany.,Forschungszentrum Jülich, Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Jülich, Germany
| | - Günther Schmalzing
- Institute of Clinical Pharmacology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
| | - Angelika Lampert
- Institute of Physiology, Uniklinik RWTH Aachen University, Pauwelsstrasse 30, Aachen, Deutschland, 52074, Germany
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25
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Nakajima T, Kaneko Y, Dharmawan T, Kurabayashi M. Role of the voltage sensor module in Na v domain IV on fast inactivation in sodium channelopathies: The implication of closed-state inactivation. Channels (Austin) 2020; 13:331-343. [PMID: 31357904 PMCID: PMC6713248 DOI: 10.1080/19336950.2019.1649521] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The segment 4 (S4) voltage sensor in voltage-gated sodium channels (Navs) have domain-specific functions, and the S4 segment in domain DIV (DIVS4) plays a key role in the activation and fast inactivation processes through the coupling of arginine residues in DIVS4 with residues of putative gating charge transfer center (pGCTC) in DIVS1-3. In addition, the first four arginine residues (R1-R4) in Nav DIVS4 have position-specific functions in the fast inactivation process, and mutations in these residues are associated with diverse phenotypes of Nav-related diseases (sodium channelopathies). R1 and R2 mutations commonly display a delayed fast inactivation, causing a gain-of-function, whereas R3 and R4 mutations commonly display a delayed recovery from inactivation and profound use-dependent current attenuation, causing a severe loss-of-function. In contrast, mutations of residues of pGCTC in Nav DIVS1-3 can also alter fast inactivation. Such alterations in fast inactivation may be caused by disrupted interactions of DIVS4 with DIVS1-3. Despite fast inactivation of Navs occurs from both the open-state (open-state inactivation; OSI) and closed state (closed-state inactivation; CSI), changes in CSI have received considerably less attention than those in OSI in the pathophysiology of sodium channelopathies. CSI can be altered by mutations of arginine residues in DIVS4 and residues of pGCTC in Navs, and altered CSI can be an underlying primary biophysical defect of sodium channelopathies. Therefore, CSI should receive focus in order to clarify the pathophysiology of sodium channelopathies.
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Affiliation(s)
- Tadashi Nakajima
- a Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine , Maebashi , Gunma , Japan
| | - Yoshiaki Kaneko
- a Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine , Maebashi , Gunma , Japan
| | - Tommy Dharmawan
- a Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine , Maebashi , Gunma , Japan
| | - Masahiko Kurabayashi
- a Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine , Maebashi , Gunma , Japan
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26
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Cowgill J, Chanda B. The contribution of voltage clamp fluorometry to the understanding of channel and transporter mechanisms. J Gen Physiol 2019; 151:1163-1172. [PMID: 31431491 PMCID: PMC6785729 DOI: 10.1085/jgp.201912372] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Cowgill and Chanda discuss the importance of voltage clamp fluorometry to the functional interpretation of ion channel and transporter structures. Key advances in single particle cryo-EM methods in the past decade have ushered in a resolution revolution in modern biology. The structures of many ion channels and transporters that were previously recalcitrant to crystallography have now been solved. Yet, despite having atomistic models of many complexes, some in multiple conformations, it has been challenging to glean mechanistic insight from these structures. To some extent this reflects our inability to unambiguously assign a given structure to a particular physiological state. One approach that may allow us to bridge this gap between structure and function is voltage clamp fluorometry (VCF). Using this technique, dynamic conformational changes can be measured while simultaneously monitoring the functional state of the channel or transporter. Many of the important papers that have used VCF to probe the gating mechanisms of channels and transporters have been published in the Journal of General Physiology. In this review, we provide an overview of the development of VCF and discuss some of the key problems that have been addressed using this approach. We end with a brief discussion of the outlook for this technique in the era of high-resolution structures.
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Affiliation(s)
- John Cowgill
- Graduate Program in Biophysics, University of Wisconsin, Madison, WI.,Department of Neuroscience, University of Wisconsin, Madison, WI
| | - Baron Chanda
- Department of Neuroscience, University of Wisconsin, Madison, WI .,Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI
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27
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Clerx M, Beattie KA, Gavaghan DJ, Mirams GR. Four Ways to Fit an Ion Channel Model. Biophys J 2019; 117:2420-2437. [PMID: 31493859 PMCID: PMC6990153 DOI: 10.1016/j.bpj.2019.08.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 06/20/2019] [Accepted: 08/01/2019] [Indexed: 12/16/2022] Open
Abstract
Mathematical models of ionic currents are used to study the electrophysiology of the heart, brain, gut, and several other organs. Increasingly, these models are being used predictively in the clinic, for example, to predict the risks and results of genetic mutations, pharmacological treatments, or surgical procedures. These safety-critical applications depend on accurate characterization of the underlying ionic currents. Four different methods can be found in the literature to fit voltage-sensitive ion channel models to whole-cell current measurements: method 1, fitting model equations directly to time-constant, steady-state, and I-V summary curves; method 2, fitting by comparing simulated versions of these summary curves to their experimental counterparts; method 3, fitting to the current traces themselves from a range of protocols; and method 4, fitting to a single current trace from a short and rapidly fluctuating voltage-clamp protocol. We compare these methods using a set of experiments in which hERG1a current was measured in nine Chinese hamster ovary cells. In each cell, the same sequence of fitting protocols was applied, as well as an independent validation protocol. We show that methods 3 and 4 provide the best predictions on the independent validation set and that short, rapidly fluctuating protocols like that used in method 4 can replace much longer conventional protocols without loss of predictive ability. Although data for method 2 are most readily available from the literature, we find it performs poorly compared to methods 3 and 4 both in accuracy of predictions and computational efficiency. Our results demonstrate how novel experimental and computational approaches can improve the quality of model predictions in safety-critical applications.
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Affiliation(s)
- Michael Clerx
- Computational Biology & Health Informatics, Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - Kylie A Beattie
- Computational Biology & Health Informatics, Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - David J Gavaghan
- Computational Biology & Health Informatics, Department of Computer Science, University of Oxford, Oxford, United Kingdom
| | - Gary R Mirams
- Centre for Mathematical Medicine & Biology, School of Mathematical Sciences, University of Nottingham, Nottingham, United Kingdom.
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28
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Tikhonov DB, Zhorov BS. Intersegment contacts determine geometry of the open and closed states in P-loop channels. J Biomol Struct Dyn 2019; 38:1012-1027. [DOI: 10.1080/07391102.2019.1592026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Denis B. Tikhonov
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russian Federation
| | - Boris S. Zhorov
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russian Federation
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
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29
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Dharmawan T, Nakajima T, Iizuka T, Tamura S, Matsui H, Kaneko Y, Kurabayashi M. Enhanced closed-state inactivation of mutant cardiac sodium channels (SCN5A N1541D and R1632C) through different mechanisms. J Mol Cell Cardiol 2019; 130:88-95. [PMID: 30935997 DOI: 10.1016/j.yjmcc.2019.03.023] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/26/2018] [Revised: 03/27/2019] [Accepted: 03/29/2019] [Indexed: 12/19/2022]
Abstract
BACKGROUND SCN5A variants can be associated with overlapping phenotypes such as Brugada syndrome (BrS), sinus node dysfunction and supraventricular tachyarrhythmias. Our genetic screening of SCN5A in 65 consecutive BrS probands revealed two patients with overlapping phenotypes: one carried an SCN5A R1632C (in domain IV-segment 4), which we have previously reported, the other carried a novel SCN5A N1541D (in domain IV-segment 1). OBJECTIVE We sought to reveal whether or not these variants are associated with the same biophysical defects. METHODS Wild-type (WT) or mutant SCN5A was expressed in tsA201-cells, and whole-cell sodium currents (hNav1.5/INa) were recorded using patch-clamp techniques. RESULTS The N1541D-INa density, when assessed from a holding potential of -150 mV, was not different from WT-INa as with R1632C-INa, indicating that SCN5A N1541D did not cause trafficking defects. The steady-state inactivation curve of N1541D-INa was markedly shifted to hyperpolarizing potentials in comparison to WT-INa (V1/2-WT: -82.3 ± 0.9 mV, n = 15; N1541D: -108.8 ± 1.6 mV, n = 26, P < .01) as with R1632C-INa. Closed-state inactivation (CSI) was evaluated using prepulses of -90 mV for 1460 ms. Residual N1541D-INa and R1632C-INa were markedly reduced in comparison to WT-INa (WT: 63.8 ± 4.6%, n = 18; N1541D: 15.1 ± 2.3%, n = 19, P < .01 vs WT; R1632C: 5.3 ± 0.5%, n = 15, P < .01 vs WT). Entry into CSI of N1541D-INa was markedly accelerated, and that of R1632C-INa was weakly accelerated in comparison to WT-INa (tau-WT: 65.8 ± 7.4 ms, n = 18; N1541D: 13.7 ± 1.1 ms, n = 19, P < .01 vs WT; R1632C: 39.5 ± 2.9 ms, n = 15, P < .01 vs WT and N1541D). Although N1541D-INa recovered from closed-state fast inactivation at the same rate as WT-INa, R1632C-INa recovered very slowly (tau-WT: 1.90 ± 0.16 ms, n = 10; N1541D: 1.72 ± 0.12 ms, n = 10, P = .41 vs WT; R1632C: 53.0 ± 2.5 ms, n = 14, P < .01 vs WT and N1541D). CONCLUSIONS Both N1541D-INa and R1632C-INa exhibited marked enhancement of CSI, but through different mechanisms. The data provided a novel understanding of the mechanisms of CSI of INa. Clinically, the enhanced CSI of N1541D-INa leads to a severe loss-of-function of INa at voltages near the physiological resting membrane potential (~-90 mV) of cardiac myocytes; this can be attributable to the patient's phenotypic manifestations.
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Affiliation(s)
- Tommy Dharmawan
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Tadashi Nakajima
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan.
| | - Takashi Iizuka
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Shuntaro Tamura
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Hiroki Matsui
- Department of Laboratory Sciences, Gunma University Graduate School of Health Sciences, Maebashi, Gunma, Japan
| | - Yoshiaki Kaneko
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
| | - Masahiko Kurabayashi
- Department of Cardiovascular Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
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30
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Abstract
A voltage change across a membrane protein moves charges or dipoles producing a gating current that is an electrical expression of a conformational change. Many membrane proteins sense the voltage across the membrane where they are inserted, and their function is affected by voltage changes. The voltage sensor consists of charges or dipoles that move in response to changes in the electric field, and their movement produces an electric current that has been called gating current. In the case of voltage-gated ion channels, the kinetic and steady-state properties of the gating charges provide information of conformational changes between closed states that are not visible when observing ionic currents only. In this Journal of General Physiology Milestone, the basic principles of voltage sensing and gating currents are presented, followed by a historical description of the recording of gating currents. The results of gating current recordings are then discussed in the context of structural changes in voltage-dependent membrane proteins and how these studies have provided new insights on gating mechanisms.
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Affiliation(s)
- Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL
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31
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Gardill BR, Rivera-Acevedo RE, Tung CC, Okon M, McIntosh LP, Van Petegem F. The voltage-gated sodium channel EF-hands form an interaction with the III-IV linker that is disturbed by disease-causing mutations. Sci Rep 2018; 8:4483. [PMID: 29540853 PMCID: PMC5852250 DOI: 10.1038/s41598-018-22713-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2017] [Accepted: 02/27/2018] [Indexed: 12/20/2022] Open
Abstract
Voltage-gated sodium channels (NaV) are responsible for the rapid depolarization of many excitable cells. They readily inactivate, a process where currents diminish after milliseconds of channel opening. They are also targets for a multitude of disease-causing mutations, many of which have been shown to affect inactivation. A cluster of disease mutations, linked to Long-QT and Brugada syndromes, is located in a C-terminal EF-hand like domain of NaV1.5, the predominant cardiac sodium channel isoform. Previous studies have suggested interactions with the III-IV linker, a cytosolic element directly involved in inactivation. Here we validate and map the interaction interface using isothermal titration calorimetry (ITC) and NMR spectroscopy. We investigated the impact of various disease mutations on the stability of the domain, and found that mutations that cause misfolding of the EF-hand domain result in hyperpolarizing shifts in the steady-state inactivation curve. Conversely, mutations in the III-IV linker that disrupt the interaction with the EF-hand domain also result in large hyperpolarization shifts, supporting the interaction between both elements in intact channels. Disrupting the interaction also causes large late currents, pointing to a dual role of the interaction in reducing the population of channels entering inactivation and in stabilizing the inactivated state.
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Affiliation(s)
- Bernd R Gardill
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Ricardo E Rivera-Acevedo
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
- Department of Anesthesiology, Pharmacology, and Therapeutics, The University of British Columbia, 2176 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Ching-Chieh Tung
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Mark Okon
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
- Department of Chemistry, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Lawrence P McIntosh
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
- Department of Chemistry, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, BC, V6T 1Z3, Canada.
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32
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Bang S, Yoo J, Gong X, Liu D, Han Q, Luo X, Chang W, Chen G, Im ST, Kim YH, Strong JA, Zhang MZ, Zhang JM, Lee SY, Ji RR. Differential Inhibition of Nav1.7 and Neuropathic Pain by Hybridoma-Produced and Recombinant Monoclonal Antibodies that Target Nav1.7 : Differential activities of Nav1.7-targeting monoclonal antibodies. Neurosci Bull 2018; 34:22-41. [PMID: 29333591 PMCID: PMC5799132 DOI: 10.1007/s12264-018-0203-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Accepted: 12/18/2017] [Indexed: 12/21/2022] Open
Abstract
The voltage-gated Na+ channel subtype Nav1.7 is important for pain and itch in rodents and humans. We previously showed that a Nav1.7-targeting monoclonal antibody (SVmab) reduces Na+ currents and pain and itch responses in mice. Here, we investigated whether recombinant SVmab (rSVmab) binds to and blocks Nav1.7 similar to SVmab. ELISA tests revealed that SVmab was capable of binding to Nav1.7-expressing HEK293 cells, mouse DRG neurons, human nerve tissue, and the voltage-sensor domain II of Nav1.7. In contrast, rSVmab showed no or weak binding to Nav1.7 in these tests. Patch-clamp recordings showed that SVmab, but not rSVmab, markedly inhibited Na+ currents in Nav1.7-expressing HEK293 cells. Notably, electrical field stimulation increased the blocking activity of SVmab and rSVmab in Nav1.7-expressing HEK293 cells. SVmab was more effective than rSVmab in inhibiting paclitaxel-induced mechanical allodynia. SVmab also bound to human DRG neurons and inhibited their Na+ currents. Finally, potential reasons for the differential efficacy of SVmab and rSVmab and future directions are discussed.
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Affiliation(s)
- Sangsu Bang
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
| | - Jiho Yoo
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA
| | - Xingrui Gong
- Pain Research Center, Department of Anesthesiology, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH, 45267-0531, USA
- Department of Anesthesiology, Shanghai Children's Medical Center, Shanghai, 200127, China
| | - Di Liu
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
| | - Qingjian Han
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
| | - Xin Luo
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
| | - Wonseok Chang
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
- Department of Physiology and Biophysics, College of Medicine, Eulji University, 143-5 Yongdu-Dong, Jung-Gu, Daejeon, 34824, Korea
| | - Gang Chen
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
| | - Sang-Taek Im
- Department of Physiology, College of Medicine, Gachon University, Incheon, 21999, Korea
| | - Yong Ho Kim
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA
- Department of Physiology, College of Medicine, Gachon University, Incheon, 21999, Korea
| | - Judith A Strong
- Pain Research Center, Department of Anesthesiology, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH, 45267-0531, USA
| | - Ma-Zhong Zhang
- Department of Anesthesiology, Shanghai Children's Medical Center, Shanghai, 200127, China
| | - Jun-Ming Zhang
- Pain Research Center, Department of Anesthesiology, University of Cincinnati, 231 Albert Sabin Way, Cincinnati, OH, 45267-0531, USA.
| | - Seok-Yong Lee
- Department of Biochemistry, Duke University Medical Center, 303 Research Drive, Durham, NC, 27710, USA.
| | - Ru-Rong Ji
- Department of Anesthesiology, Duke University Medical Center, 595 LaSalle St, Durham, NC, 27710, USA.
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33
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Silva JR. How to Connect Cardiac Excitation to the Atomic Interactions of Ion Channels. Biophys J 2018; 114:259-266. [PMID: 29401425 PMCID: PMC5984968 DOI: 10.1016/j.bpj.2017.11.024] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2017] [Revised: 10/09/2017] [Accepted: 11/16/2017] [Indexed: 12/26/2022] Open
Abstract
Many have worked to create cardiac action potential models that explicitly represent atomic-level details of ion channel structure. Such models have the potential to define new therapeutic directions and to show how nanoscale perturbations to channel function predispose patients to deadly cardiac arrhythmia. However, there have been significant experimental and theoretical barriers that have limited model usefulness. Recently, many of these barriers have come down, suggesting that considerable progress toward creating these long-sought models may be possible in the near term.
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Affiliation(s)
- Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri.
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34
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Distinct modulation of inactivation by a residue in the pore domain of voltage-gated Na + channels: mechanistic insights from recent crystal structures. Sci Rep 2018; 8:631. [PMID: 29330525 PMCID: PMC5766632 DOI: 10.1038/s41598-017-18919-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 12/18/2017] [Indexed: 12/19/2022] Open
Abstract
Inactivation of voltage-gated Na+ channels (VGSC) is essential for the regulation of cellular excitability. The molecular rearrangement underlying inactivation is thought to involve the intracellular linker between domains III and IV serving as inactivation lid, the receptor for the lid (domain III S4-S5 linker) and the pore-lining S6 segements. To better understand the role of the domain IV S6 segment in inactivation we performed a cysteine scanning mutagenesis of this region in rNav 1.4 channels and screened the constructs for perturbations in the voltage-dependence of steady state inactivation. This screen was performed in the background of wild-type channels and in channels carrying the mutation K1237E, which profoundly alters both permeation and gating-properties. Of all tested constructs the mutation I1581C was unique in that the mutation-induced gating changes were strongly influenced by the mutational background. This suggests that I1581 is involved in specific short-range interactions during inactivation. In recently published crystal structures VGSCs the respective amino acids homologous to I1581 appear to control a bend of the S6 segment which is critical to the gating process. Furthermore, I1581 may be involved in the transmission of the movement of the DIII voltage-sensor to the domain IV S6 segment.
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35
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Gilchrist J, Bosmans F. Using voltage-sensor toxins and their molecular targets to investigate Na V 1.8 gating. J Physiol 2018; 596:1863-1872. [PMID: 29193176 DOI: 10.1113/jp275102] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2017] [Accepted: 11/16/2017] [Indexed: 01/10/2023] Open
Abstract
Voltage-gated sodium (NaV ) channel gating is a complex phenomenon which involves a distinct contribution of four integral voltage-sensing domains (VSDI, VSDII, VSDIII and VSDIV). Utilizing accrued pharmacological and structural insights, we build on an established chimera approach to introduce animal toxin sensitivity in each VSD of an acceptor channel by transferring in portable S3b-S4 motifs from the four VSDs of a toxin-susceptible donor channel (NaV 1.2). By doing so, we observe that in NaV 1.8, a relatively unexplored channel subtype with distinctly slow gating kinetics, VSDI-III participate in channel opening whereas VSDIV can regulate opening as well as fast inactivation. These results illustrate the effectiveness of a pharmacological approach to investigate the mechanism underlying gating of a mammalian NaV channel complex.
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Affiliation(s)
- John Gilchrist
- Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, MD, 21205, USA
| | - Frank Bosmans
- Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, MD, 21205, USA.,Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD, 21205, USA
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36
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Abstract
Voltage-gated sodium (Na+) channels are expressed in virtually all electrically excitable tissues and are essential for muscle contraction and the conduction of impulses within the peripheral and central nervous systems. Genetic disorders that disrupt the function of these channels produce an array of Na+ channelopathies resulting in neuronal impairment, chronic pain, neuromuscular pathologies, and cardiac arrhythmias. Because of their importance to the conduction of electrical signals, Na+ channels are the target of a wide variety of local anesthetic, antiarrhythmic, anticonvulsant, and antidepressant drugs. The voltage-gated family of Na+ channels is composed of α-subunits that encode for the voltage sensor domains and the Na+-selective permeation pore. In vivo, Na+ channel α-subunits are associated with one or more accessory β-subunits (β1-β4) that regulate gating properties, trafficking, and cell-surface expression of the channels. The permeation pore of Na+ channels is divided in two parts: the outer mouth of the pore is the site of the ion selectivity filter, while the inner cytoplasmic pore serves as the channel activation gate. The cytoplasmic lining of the permeation pore is formed by the S6 segments that include highly conserved aromatic amino acids important for drug binding. These residues are believed to undergo voltage-dependent conformational changes that alter drug binding as the channels cycle through the closed, open, and inactivated states. The purpose of this chapter is to broadly review the mechanisms of Na+ channel gating and the models used to describe drug binding and Na+ channel inhibition.
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Affiliation(s)
- M E O'Leary
- Cooper Medical School of Rowan University, Camden, NJ, USA
| | - M Chahine
- CERVO Brain Research Center, Institut universitaire en santé mentale de Québec, Quebec City, QC, Canada.
- Department of Medicine, Université Laval, Quebec City, QC, Canada.
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37
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Abstract
Voltage-gated sodium channels belong to the superfamily of voltage-gated cation channels. Their structure is based on domains comprising a voltage sensor domain (S1-S4 segments) and a pore domain (S5-S6 segments). Mutations in positively charged residues of the S4 segments may allow protons or cations to pass directly through the gating pore constriction of the voltage sensor domain; these anomalous currents are referred to as gating pore or omega (ω) currents. In the skeletal muscle disorder hypokalemic periodic paralysis, and in arrhythmic dilated cardiomyopathy, inherited mutations of S4 arginine residues promote omega currents that have been shown to be a contributing factor in the pathogenesis of these sodium channel disorders. Characterization of gating pore currents in these channelopathies and with artificial mutations has been possible by measuring the voltage-dependence and selectivity of these leak currents. The basis of gating pore currents and the structural basis of S4 movement through the gating pore has also been studied extensively with molecular dynamics. These simulations have provided valuable insight into the nature of S4 translocation and the physical basis for the effects of mutations that promote permeation of protons or cations through the gating pore.
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Affiliation(s)
- J R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID, 83209, USA.
| | - A Moreau
- Institut NeuroMyogene, ENS de Lyon, Site MONOD, Lyon, France
| | - L Delemotte
- Science for Life Laboratory, Department of Physics, KTH Royal Institute of Technology, Box 1031, 171 21, Solna, Sweden
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38
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Salari S, Silverå Ejneby M, Brask J, Elinder F. Isopimaric acid - a multi-targeting ion channel modulator reducing excitability and arrhythmicity in a spontaneously beating mouse atrial cell line. Acta Physiol (Oxf) 2018; 222. [PMID: 28514017 DOI: 10.1111/apha.12895] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2017] [Revised: 03/08/2017] [Accepted: 05/12/2017] [Indexed: 11/28/2022]
Abstract
AIM Atrial fibrillation is the most common persistent cardiac arrhythmia, and it is not well controlled by present drugs. Because some resin acids open voltage-gated potassium channels and reduce neuronal excitability, we explored the effects of the resin acid isopimaric acid (IPA) on action potentials and ion currents in cardiomyocytes. METHODS Spontaneously beating mouse atrial HL-1 cells were investigated with the whole-cell patch-clamp technique. RESULTS 1-25 μmol L-1 IPA reduced the action potential frequency by up to 50%. The effect of IPA on six different voltage-gated ion channels was investigated; most voltage-dependent parameters of ion channel gating were shifted in the negative direction along the voltage axis, consistent with a hypothesis that a lipophilic and negatively charged compound binds to the lipid membrane close to the positively charged voltage sensor of the ion channels. The major finding was that IPA inactivated sodium channels and L- and T-type calcium channels and activated the rapidly activating potassium channel and the transient outward potassium channel. Computer simulations of IPA effects on all of the ion currents were consistent with a reduced excitability, and they also showed that effects on the Na channel played the largest role to reduce the action potential frequency. Finally, induced arrhythmia in the HL-1 cells was reversed by IPA. CONCLUSION Low concentrations of IPA reduced the action potential frequency and restored regular firing by altering the voltage dependencies of several voltage-gated ion channels. These findings can form the basis for a new pharmacological strategy to treat atrial fibrillation.
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Affiliation(s)
- S. Salari
- Department of Clinical and Experimental Medicine; Linköping University; Linköping Sweden
| | - M. Silverå Ejneby
- Department of Clinical and Experimental Medicine; Linköping University; Linköping Sweden
| | - J. Brask
- Department of Clinical and Experimental Medicine; Linköping University; Linköping Sweden
| | - F. Elinder
- Department of Clinical and Experimental Medicine; Linköping University; Linköping Sweden
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39
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Abstract
Armstrong and Hollingworth discuss inactivation in the light of modern structural data from K and Na channels. We are wired with conducting cables called axons that rapidly transmit electrical signals (e.g., “Ouch!”) from, for example, the toe to the spinal cord. Because of the high internal resistance of axons (salt water rather than copper), a signal must be reinforced after traveling a short distance. Reinforcement is accomplished by ion channels, Na channels for detecting the signal and reinforcing it by driving it further positive (to near 50 mV) and K channels for then restoring it to the resting level (near −70 mV). The signal is called an action potential and has a duration of roughly a millisecond. The return of membrane voltage (Vm) to the resting level after an action potential is facilitated by “inactivation” of the Na channels: i.e., an internal particle diffuses into the mouth of any open Na channel and temporarily blocks it. Some types of K channels also show inactivation after being open for a time. N-type inactivation of K channels has a relatively fast time course and involves diffusion of the N-terminal of one of the channel’s four identical subunits into the channel’s inner mouth, if it is open. This mechanism is similar to Na channel inactivation. Both Na and K channels also display slower inactivation processes. C inactivation in K channels involves changes in the channel’s outer mouth, the “selectivity filter,” whose normal function is to prevent Na+ ions from entering the K channel. C inactivation deforms the filter so that neither K+ nor Na+ can pass.
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Affiliation(s)
- Clay M Armstrong
- Department of Physiology, University of Pennsylvania, Philadelphia, PA
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40
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Savalli N, Pantazis A, Sigg D, Weiss JN, Neely A, Olcese R. The α2δ-1 subunit remodels CaV1.2 voltage sensors and allows Ca2+ influx at physiological membrane potentials. J Gen Physiol 2017; 148:147-59. [PMID: 27481713 PMCID: PMC4969795 DOI: 10.1085/jgp.201611586] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 06/30/2016] [Indexed: 12/30/2022] Open
Abstract
Voltage-sensing domains (VSDs) in voltage-gated calcium channels sense the potential difference across membranes and interact with the pore to open it. Savalli et al. find that the accessory subunit α2δ-1 increases the sensitivity of VSDs I–III and also their efficiency of coupling to the pore. Excitation-evoked calcium influx across cellular membranes is strictly controlled by voltage-gated calcium channels (CaV), which possess four distinct voltage-sensing domains (VSDs) that direct the opening of a central pore. The energetic interactions between the VSDs and the pore are critical for tuning the channel’s voltage dependence. The accessory α2δ-1 subunit is known to facilitate CaV1.2 voltage-dependent activation, but the underlying mechanism is unknown. In this study, using voltage clamp fluorometry, we track the activation of the four individual VSDs in a human L-type CaV1.2 channel consisting of α1C and β3 subunits. We find that, without α2δ-1, the channel complex displays a right-shifted voltage dependence such that currents mainly develop at nonphysiological membrane potentials because of very weak VSD–pore interactions. The presence of α2δ-1 facilitates channel activation by increasing the voltage sensitivity (i.e., the effective charge) of VSDs I–III. Moreover, the α2δ-1 subunit also makes VSDs I–III more efficient at opening the channel by increasing the coupling energy between VSDs II and III and the pore, thus allowing Ca influx within the range of physiological membrane potentials.
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Affiliation(s)
- Nicoletta Savalli
- Department of Anesthesiology, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | - Antonios Pantazis
- Department of Anesthesiology, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | | | - James N Weiss
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | - Alan Neely
- Department of Anesthesiology, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Centro Interdisciplinario de Neurociencias de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360102, Chile
| | - Riccardo Olcese
- Department of Anesthesiology, Division of Molecular Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095 Cardiovascular Research Laboratories, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
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41
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Mangold KE, Brumback BD, Angsutararux P, Voelker TL, Zhu W, Kang PW, Moreno JD, Silva JR. Mechanisms and models of cardiac sodium channel inactivation. Channels (Austin) 2017; 11:517-533. [PMID: 28837385 PMCID: PMC5786193 DOI: 10.1080/19336950.2017.1369637] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 08/14/2017] [Accepted: 08/15/2017] [Indexed: 12/19/2022] Open
Abstract
Shortly after cardiac Na+ channels activate and initiate the action potential, inactivation ensues within milliseconds, attenuating the peak Na+ current, INa, and allowing the cell membrane to repolarize. A very limited number of Na+ channels that do not inactivate carry a persistent INa, or late INa. While late INa is only a small fraction of peak magnitude, it significantly prolongs ventricular action potential duration, which predisposes patients to arrhythmia. Here, we review our current understanding of inactivation mechanisms, their regulation, and how they have been modeled computationally. Based on this body of work, we conclude that inactivation and its connection to late INa would be best modeled with a "feet-on-the-door" approach where multiple channel components participate in determining inactivation and late INa. This model reflects experimental findings showing that perturbation of many channel locations can destabilize inactivation and cause pathological late INa.
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Affiliation(s)
- Kathryn E. Mangold
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Brittany D. Brumback
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Paweorn Angsutararux
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Taylor L. Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Po Wei Kang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Jonathan D. Moreno
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Jonathan R. Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, USA
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42
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Peters CH, Yu A, Zhu W, Silva JR, Ruben PC. Depolarization of the conductance-voltage relationship in the NaV1.5 mutant, E1784K, is due to altered fast inactivation. PLoS One 2017; 12:e0184605. [PMID: 28898267 PMCID: PMC5595308 DOI: 10.1371/journal.pone.0184605] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 08/28/2017] [Indexed: 12/19/2022] Open
Abstract
E1784K is the most common mixed long QT syndrome/Brugada syndrome mutant in the cardiac voltage-gated sodium channel NaV1.5. E1784K shifts the midpoint of the channel conductance-voltage relationship to more depolarized membrane potentials and accelerates the rate of channel fast inactivation. The depolarizing shift in the midpoint of the conductance curve in E1784K is exacerbated by low extracellular pH. We tested whether the E1784K mutant shifts the channel conductance curve to more depolarized membrane potentials by affecting the channel voltage-sensors. We measured ionic currents and gating currents at pH 7.4 and pH 6.0 in Xenopus laevis oocytes. Contrary to our expectation, the movement of gating charges is shifted to more hyperpolarized membrane potentials by E1784K. Voltage-clamp fluorimetry experiments show that this gating charge shift is due to the movement of the DIVS4 voltage-sensor being shifted to more hyperpolarized membrane potentials. Using a model and experiments on fast inactivation-deficient channels, we show that changes to the rate and voltage-dependence of fast inactivation are sufficient to shift the conductance curve in E1784K. Our results localize the effects of E1784K to DIVS4, and provide novel insight into the role of the DIV-VSD in regulating the voltage-dependencies of activation and fast inactivation.
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Affiliation(s)
- Colin H. Peters
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Alec Yu
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Jonathan R. Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Peter C. Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
- * E-mail:
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43
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Zhu W, Voelker TL, Varga Z, Schubert AR, Nerbonne JM, Silva JR. Mechanisms of noncovalent β subunit regulation of Na V channel gating. J Gen Physiol 2017; 149:813-831. [PMID: 28720590 PMCID: PMC5560778 DOI: 10.1085/jgp.201711802] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 06/26/2017] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated NaV channels are modulated by two different noncovalent accessory subunits: β1 and β3. Zhu et al. present data showing that β1 and β3 cause distinct effects on channel gating because they interact with NaV channels at different locations. β3 regulates the voltage sensor in domain III, whereas β1 regulates the one in domain IV. Voltage-gated Na+ (NaV) channels comprise a macromolecular complex whose components tailor channel function. Key components are the non-covalently bound β1 and β3 subunits that regulate channel gating, expression, and pharmacology. Here, we probe the molecular basis of this regulation by applying voltage clamp fluorometry to measure how the β subunits affect the conformational dynamics of the cardiac NaV channel (NaV1.5) voltage-sensing domains (VSDs). The pore-forming NaV1.5 α subunit contains four domains (DI–DIV), each with a VSD. Our results show that β1 regulates NaV1.5 by modulating the DIV-VSD, whereas β3 alters channel kinetics mainly through DIII-VSD interaction. Introduction of a quenching tryptophan into the extracellular region of the β3 transmembrane segment inverted the DIII-VSD fluorescence. Additionally, a fluorophore tethered to β3 at the same position produced voltage-dependent fluorescence dynamics strongly resembling those of the DIII-VSD. Together, these results provide compelling evidence that β3 binds proximally to the DIII-VSD. Molecular-level differences in β1 and β3 interaction with the α subunit lead to distinct activation and inactivation recovery kinetics, significantly affecting NaV channel regulation of cell excitability.
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Affiliation(s)
- Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Taylor L Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Zoltan Varga
- MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, University of Debrecen, Debrecen, Hungary
| | - Angela R Schubert
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO.,Department of Internal Medicine, Washington University in St. Louis, St. Louis, MO
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
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44
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Pharmacology of the Na v1.1 domain IV voltage sensor reveals coupling between inactivation gating processes. Proc Natl Acad Sci U S A 2017; 114:6836-6841. [PMID: 28607094 DOI: 10.1073/pnas.1621263114] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Nav1.1 voltage-gated sodium channel is a critical contributor to excitability in the brain, where pathological loss of function leads to such disorders as epilepsy, Alzheimer's disease, and autism. This voltage-gated sodium (Nav) channel subtype also plays an important role in mechanical pain signaling by primary afferent somatosensory neurons. Therefore, pharmacologic modulation of Nav1.1 represents a potential strategy for treating excitability disorders of the brain and periphery. Inactivation is a complex aspect of Nav channel gating and consists of fast and slow components, each of which may involve a contribution from one or more voltage-sensing domains. Here, we exploit the Hm1a spider toxin, a Nav1.1-selective modulator, to better understand the relationship between these temporally distinct modes of inactivation and ask whether they can be distinguished pharmacologically. We show that Hm1a inhibits the gating movement of the domain IV voltage sensor (VSDIV), hindering both fast and slow inactivation and leading to an increase in Nav1.1 availability during high-frequency stimulation. In contrast, ICA-121431, a small-molecule Nav1.1 inhibitor, accelerates a subsequent VSDIV gating transition to accelerate entry into the slow inactivated state, resulting in use-dependent block. Further evidence for functional coupling between fast and slow inactivation is provided by a Nav1.1 mutant in which fast inactivation removal has complex effects on slow inactivation. Taken together, our data substantiate the key role of VSDIV in Nav channel fast and slow inactivation and demonstrate that these gating processes are sequential and coupled through VSDIV. These findings provide insight into a pharmacophore on VSDIV through which modulation of inactivation gating can inhibit or facilitate Nav1.1 function.
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45
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Hsu EJ, Zhu W, Schubert AR, Voelker T, Varga Z, Silva JR. Regulation of Na + channel inactivation by the DIII and DIV voltage-sensing domains. J Gen Physiol 2017; 149:389-403. [PMID: 28232510 PMCID: PMC5339511 DOI: 10.1085/jgp.201611678] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 12/02/2016] [Accepted: 01/20/2017] [Indexed: 12/19/2022] Open
Abstract
Functional eukaryotic voltage-gated Na+ (NaV) channels comprise four domains (DI-DIV), each containing six membrane-spanning segments (S1-S6). Voltage sensing is accomplished by the first four membrane-spanning segments (S1-S4), which together form a voltage-sensing domain (VSD). A critical NaV channel gating process, inactivation, has previously been linked to activation of the VSDs in DIII and DIV. Here, we probe this interaction by using voltage-clamp fluorometry to observe VSD kinetics in the presence of mutations at locations that have been shown to impair NaV channel inactivation. These locations include the DIII-DIV linker, the DIII S4-S5 linker, and the DIV S4-S5 linker. Our results show that, within the 10-ms timeframe of fast inactivation, the DIV-VSD is the primary regulator of inactivation. However, after longer 100-ms pulses, the DIII-DIV linker slows DIII-VSD deactivation, and the rate of DIII deactivation correlates strongly with the rate of recovery from inactivation. Our results imply that, over the course of an action potential, DIV-VSDs regulate the onset of fast inactivation while DIII-VSDs determine its recovery.
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Affiliation(s)
- Eric J Hsu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO 63130
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO 63130
| | - Angela R Schubert
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO 63130
| | - Taylor Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO 63130
| | - Zoltan Varga
- MTA-DE-NAP B Ion Channel Structure-Function Research Group, Research Center for Molecular Medicine (RCMM), University of Debrecen, Debrecen H-4032, Hungary
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO 63130
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46
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Bohnen MS, Peng G, Robey SH, Terrenoire C, Iyer V, Sampson KJ, Kass RS. Molecular Pathophysiology of Congenital Long QT Syndrome. Physiol Rev 2017; 97:89-134. [PMID: 27807201 PMCID: PMC5539372 DOI: 10.1152/physrev.00008.2016] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.
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Affiliation(s)
- M S Bohnen
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - G Peng
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - S H Robey
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - C Terrenoire
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - V Iyer
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - K J Sampson
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - R S Kass
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
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47
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Vaccaro SR. Derivation of Hodgkin-Huxley equations for a Na^{+} channel from a master equation for coupled activation and inactivation. Phys Rev E 2016; 94:052407. [PMID: 27967064 DOI: 10.1103/physreve.94.052407] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Indexed: 11/07/2022]
Abstract
The Na^{+} current in nerve and muscle membranes may be described in terms of the activation variable m(t) and the inactivation variable h(t), which are dependent on the transitions of S4 sensors of each of the Na^{+} channel domains DI to DIV. The time-dependence of the Na^{+} current and the rate equations satisfied by m(t) and h(t) may be derived from the solution to a master equation that describes the coupling between two or three activation sensors regulating the Na^{+} channel conductance and a two-stage inactivation process. If the inactivation rate from the closed or open states increases as the S4 sensors activate, a more general form of the Hodgkin-Huxley expression for the open-state probability may be derived where m(t) is dependent on both activation and inactivation processes. The voltage dependence of the rate functions for inactivation and recovery from inactivation are consistent with the empirically determined expressions and exhibit saturation for both depolarized and hyperpolarized clamp potentials.
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Affiliation(s)
- S R Vaccaro
- Department of Physics, University of Adelaide, Adelaide, South Australia, 5005, Australia
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48
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Peters C, Rosch RE, Hughes E, Ruben PC. Temperature-dependent changes in neuronal dynamics in a patient with an SCN1A mutation and hyperthermia induced seizures. Sci Rep 2016; 6:31879. [PMID: 27582020 PMCID: PMC5007485 DOI: 10.1038/srep31879] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 07/28/2016] [Indexed: 01/01/2023] Open
Abstract
Dravet syndrome is the prototype of SCN1A-mutation associated epilepsies. It is characterised by prolonged seizures, typically provoked by fever. We describe the evaluation of an SCN1A mutation in a child with early-onset temperature-sensitive seizures. The patient carries a heterozygous missense variant (c3818C > T; pAla1273Val) in the NaV1.1 brain sodium channel. We compared the functional effects of the variant vs. wild type NaV1.1 using patch clamp recordings from channels expressed in Chinese Hamster Ovary Cells at different temperatures (32, 37, and 40 °C). The variant channels produced a temperature-dependent destabilization of activation and fast inactivation. Implementing these empirical abnormalities in a computational model predicts a higher threshold for depolarization block in the variant, particularly at 40 °C, suggesting a failure to autoregulate at high-input states. These results reveal direct effects of abnormalities in NaV1.1 biophysical properties on neuronal dynamics. They illustrate the value of combining cellular measurements with computational models to integrate different observational scales (gene/channel to patient).
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Affiliation(s)
- C Peters
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
| | - R E Rosch
- Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, UK.,Centre for Developmental Cognitive Neuroscience, Institute of Child Health, University College, London, UK
| | - E Hughes
- Department of Paediatric Neurology, Evelina London Children's Hospital, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - P C Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada
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49
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Pei Z, Xiao Y, Meng J, Hudmon A, Cummins TR. Cardiac sodium channel palmitoylation regulates channel availability and myocyte excitability with implications for arrhythmia generation. Nat Commun 2016; 7:12035. [PMID: 27337590 PMCID: PMC4931030 DOI: 10.1038/ncomms12035] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 05/22/2016] [Indexed: 02/06/2023] Open
Abstract
Cardiac voltage-gated sodium channels (Nav1.5) play an essential role in regulating cardiac electric activity by initiating and propagating action potentials in the heart. Altered Nav1.5 function is associated with multiple cardiac diseases including long-QT3 and Brugada syndrome. Here, we show that Nav1.5 is subject to palmitoylation, a reversible post-translational lipid modification. Palmitoylation increases channel availability and late sodium current activity, leading to enhanced cardiac excitability and prolonged action potential duration. In contrast, blocking palmitoylation increases closed-state channel inactivation and reduces myocyte excitability. We identify four cysteines as possible Nav1.5 palmitoylation substrates. A mutation of one of these is associated with cardiac arrhythmia (C981F), induces a significant enhancement of channel closed-state inactivation and ablates sensitivity to depalmitoylation. Our data indicate that alterations in palmitoylation can substantially control Nav1.5 function and cardiac excitability and this form of post-translational modification is likely an important contributor to acquired and congenital arrhythmias.
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Affiliation(s)
- Zifan Pei
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA
| | - Yucheng Xiao
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA
| | - Jingwei Meng
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA
| | - Andy Hudmon
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA.,Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA.,Stark Neurosciences Research Institute, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA
| | - Theodore R Cummins
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA.,Stark Neurosciences Research Institute, Indiana University School of Medicine, 635 Barnhill Drive, Indianapolis, Indiana 46202, USA
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Guo J, Cheng YM, Lees-Miller JP, Perissinotti LL, Claydon TW, Hull CM, Thouta S, Roach DE, Durdagi S, Noskov SY, Duff HJ. NS1643 interacts around L529 of hERG to alter voltage sensor movement on the path to activation. Biophys J 2016; 108:1400-1413. [PMID: 25809253 DOI: 10.1016/j.bpj.2014.12.055] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Revised: 11/25/2014] [Accepted: 12/08/2014] [Indexed: 12/17/2022] Open
Abstract
Activators of hERG1 such as NS1643 are being developed for congenital/acquired long QT syndrome. Previous studies identify the neighborhood of L529 around the voltage-sensor as a putative interacting site for NS1643. With NS1643, the V1/2 of activation of L529I (-34 ± 4 mV) is similar to wild-type (WT) (-37 ± 3 mV; P > 0.05). WT and L529I showed no difference in the slope factor in the absence of NS1643 (8 ± 0 vs. 9 ± 0) but showed a difference in the presence of NS1643 (9 ± 0.3 vs. 22 ± 1; P < 0.01). Voltage-clamp-fluorimetry studies also indicated that in L529I, NS1643 reduces the voltage-sensitivity of S4 movement. To further assess mechanism of NS1643 action, mutations were made in this neighborhood. NS1643 shifts the V1/2 of activation of both K525C and K525C/L529I to hyperpolarized potentials (-131 ± 4 mV for K525C and -120 ± 21 mV for K525C/L529I). Both K525C and K525C/K529I had similar slope factors in the absence of NS1643 (18 ± 2 vs. 34 ± 5, respectively) but with NS1643, the slope factor of K525C/L529I increased from 34 ± 5 to 71 ± 10 (P < 0.01) whereas for K525C the slope factor did not change (18 ± 2 at baseline and 16 ± 2 for NS1643). At baseline, K525R had a slope factor similar to WT (9 vs. 8) but in the presence of NS1643, the slope factor of K525R was increased to 24 ± 4 vs. 9 ± 0 mV for WT (P < 0.01). Molecular modeling indicates that L529I induces a kink in the S4 voltage-sensor helix, altering a salt-bridge involving K525. Moreover, docking studies indicate that NS1643 binds to the kinked structure induced by the mutation with a higher affinity. Combining biophysical, computational, and electrophysiological evidence, a mechanistic principle governing the action of some activators of hERG1 channels is proposed.
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Affiliation(s)
- Jiqing Guo
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Yen May Cheng
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - James P Lees-Miller
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Laura L Perissinotti
- Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Tom W Claydon
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Christina M Hull
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Samrat Thouta
- Department of Biomedical Physiology and Kinesiology, Molecular Cardiac Physiology Group, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Daniel E Roach
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Serdar Durdagi
- Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Sergei Y Noskov
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada; Centre for Molecular Simulations, Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
| | - Henry J Duff
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
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