1
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Kesdoğan AB, Neureiter A, Gaebler AJ, Kalia AK, Körner J, Lampert A. Analgesic effect of Botulinum toxin in neuropathic pain is sodium channel independent. Neuropharmacology 2024; 253:109967. [PMID: 38657946 DOI: 10.1016/j.neuropharm.2024.109967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 02/26/2024] [Accepted: 04/20/2024] [Indexed: 04/26/2024]
Abstract
Botulinum neurotoxin type A BoNT/A is used off-label as a third line therapy for neuropathic pain. However, the mechanism of action remains unclear. In recent years, the role of voltage-gated sodium channels (Nav) in neuropathic pain became evident and it was suggested that block of sodium channels by BoNT/A would contribute to its analgesic effect. We assessed sodium channel function in the presence of BoNT/A in heterologously expressed Nav1.7, Nav1.3, and the neuronal cell line ND7/23 by high throughput automated and manual patch-clamp. We used both the full protein and the isolated catalytic light chain LC/A for acute or long-term extracellular or intracellular exposure. To assess the toxin's effect in a human cellular system, we differentiated induced pluripotent stem cells (iPSC) into sensory neurons from a healthy control and a patient suffering from a hereditary neuropathic pain syndrome (inherited erythromelalgia) carrying the Nav1.7/p.Q875E-mutation and carried out multielectrode-array measurements. Both BoNT/A and the isolated catalytic light chain LC/A showed limited effects in heterologous expression systems and the neuronal cell line ND7/23. Spontaneous activity in iPSC derived sensory neurons remained unaltered upon BoNT/A exposure both in neurons from the healthy control and the mutation carrying patient. BoNT/A may not specifically be beneficial in pain syndromes linked to sodium channel variants. The favorable effects of BoNT/A in neuropathic pain are likely based on mechanisms other than sodium channel blockage and new approaches to understand BoNT/A's therapeutic effects are necessary.
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Affiliation(s)
- Aylin B Kesdoğan
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Anika Neureiter
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Arnim J Gaebler
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Anil K Kalia
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Jannis Körner
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Anesthesiology, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Intensive and Intermediate Care, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany.
| | - Angelika Lampert
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
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2
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Chen H, Xia Z, Dong J, Huang B, Zhang J, Zhou F, Yan R, Shi Y, Gong J, Jiang J, Huang Z, Jiang D. Structural mechanism of voltage-gated sodium channel slow inactivation. Nat Commun 2024; 15:3691. [PMID: 38693179 PMCID: PMC11063143 DOI: 10.1038/s41467-024-48125-3] [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: 07/07/2023] [Accepted: 04/17/2024] [Indexed: 05/03/2024] Open
Abstract
Voltage-gated sodium (NaV) channels mediate a plethora of electrical activities. NaV channels govern cellular excitability in response to depolarizing stimuli. Inactivation is an intrinsic property of NaV channels that regulates cellular excitability by controlling the channel availability. The fast inactivation, mediated by the Ile-Phe-Met (IFM) motif and the N-terminal helix (N-helix), has been well-characterized. However, the molecular mechanism underlying NaV channel slow inactivation remains elusive. Here, we demonstrate that the removal of the N-helix of NaVEh (NaVEhΔN) results in a slow-inactivated channel, and present cryo-EM structure of NaVEhΔN in a potential slow-inactivated state. The structure features a closed activation gate and a dilated selectivity filter (SF), indicating that the upper SF and the inner gate could serve as a gate for slow inactivation. In comparison to the NaVEh structure, NaVEhΔN undergoes marked conformational shifts on the intracellular side. Together, our results provide important mechanistic insights into NaV channel slow inactivation.
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Affiliation(s)
- Huiwen Chen
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, No. 600 Changjiang Road, Xiangfang District, Harbin, 150030, China
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
| | - Zhanyi Xia
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China
| | - Jie Dong
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Bo Huang
- Beijing StoneWise Technology Co Ltd., 15 Haidian street, Haidian district, Beijing, China
| | - Jiangtao Zhang
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- College of Life Science and Technology, Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Feng Zhou
- Beijing StoneWise Technology Co Ltd., 15 Haidian street, Haidian district, Beijing, China
| | - Rui Yan
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China
- College of Life Science and Technology, Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yiqiang Shi
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, 100191, China
| | - Jianke Gong
- College of Life Science and Technology, Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Juquan Jiang
- Department of Microbiology and Biotechnology, College of Life Sciences, Northeast Agricultural University, No. 600 Changjiang Road, Xiangfang District, Harbin, 150030, China.
| | - Zhuo Huang
- State Key Laboratory of Natural and Biomimetic Drugs, Department of Molecular and Cellular Pharmacology, School of Pharmaceutical Sciences, Peking University Health Science Center, Beijing, 100191, China.
| | - Daohua Jiang
- Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100190, China.
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3
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del Rivero Morfin PJ, Kochiss AL, Liedl KR, Flucher BE, Fernández-Quintero ML, Ben-Johny M. Asymmetric contribution of a selectivity filter gate in triggering inactivation of CaV1.3 channels. J Gen Physiol 2024; 156:e202313365. [PMID: 38175169 PMCID: PMC10771039 DOI: 10.1085/jgp.202313365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 10/08/2023] [Accepted: 12/14/2023] [Indexed: 01/05/2024] Open
Abstract
Voltage-dependent and Ca2+-dependent inactivation (VDI and CDI, respectively) of CaV channels are two biologically consequential feedback mechanisms that fine-tune Ca2+ entry into neurons and cardiomyocytes. Although known to be initiated by distinct molecular events, how these processes obstruct conduction through the channel pore remains poorly defined. Here, focusing on ultrahighly conserved tryptophan residues in the interdomain interfaces near the selectivity filter of CaV1.3, we demonstrate a critical role for asymmetric conformational changes in mediating VDI and CDI. Specifically, mutagenesis of the domain III-IV interface, but not others, enhanced VDI. Molecular dynamics simulations demonstrate that mutations in distinct selectivity filter interfaces differentially impact conformational flexibility. Furthermore, mutations in distinct domains preferentially disrupt CDI mediated by the N- versus C-lobes of CaM, thus uncovering a scheme of structural bifurcation of CaM signaling. These findings highlight the fundamental importance of the asymmetric arrangement of the pseudotetrameric CaV pore domain for feedback inhibition.
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Affiliation(s)
| | - Audrey L. Kochiss
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA
| | - Klaus R. Liedl
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Bernhard E. Flucher
- Department of Physiology and Medical Physics, Institute of Physiology, Medical University Innsbruck, Innsbruck, Austria
| | | | - Manu Ben-Johny
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA
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4
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del Rivero Morfin PJ, Kochiss AL, Liedl KR, Flucher BE, Fernández-Quintero ML, Ben-Johny M. Asymmetric Contribution of a Selectivity Filter Gate in Triggering Inactivation of Ca V1.3 Channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.21.558864. [PMID: 37790368 PMCID: PMC10542529 DOI: 10.1101/2023.09.21.558864] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
Voltage-dependent and Ca2+-dependent inactivation (VDI and CDI, respectively) of CaV channels are two biologically consequential feedback mechanisms that fine-tune Ca2+ entry into neurons and cardiomyocytes. Although known to be initiated by distinct molecular events, how these processes obstruct conduction through the channel pore remains poorly defined. Here, focusing on ultra-highly conserved tryptophan residues in the inter-domain interfaces near the selectivity filter of CaV1.3, we demonstrate a critical role for asymmetric conformational changes in mediating VDI and CDI. Specifically, mutagenesis of the domain III-IV interface, but not others, enhanced VDI. Molecular dynamics simulations demonstrate that mutations in distinct selectivity filter interfaces differentially impact conformational flexibility. Furthermore, mutations in distinct domains preferentially disrupt CDI mediated by the N- versus C-lobes of CaM, thus uncovering a scheme of structural bifurcation of CaM signaling. These findings highlight the fundamental importance of the asymmetric arrangement of the pseudo-tetrameric CaV pore domain for feedback inhibition.
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Affiliation(s)
| | - Audrey L. Kochiss
- Department of Physiology and Cellular Biophysics, Columbia University
| | - Klaus R. Liedl
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Bernhard E. Flucher
- Institute of Physiology, Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | | | - Manu Ben-Johny
- Department of Physiology and Cellular Biophysics, Columbia University
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5
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Groome JR. Historical Perspective of the Characterization of Conotoxins Targeting Voltage-Gated Sodium Channels. Mar Drugs 2023; 21:md21040209. [PMID: 37103349 PMCID: PMC10142487 DOI: 10.3390/md21040209] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Revised: 03/21/2023] [Accepted: 03/24/2023] [Indexed: 03/30/2023] Open
Abstract
Marine toxins have potent actions on diverse sodium ion channels regulated by transmembrane voltage (voltage-gated ion channels) or by neurotransmitters (nicotinic acetylcholine receptor channels). Studies of these toxins have focused on varied aspects of venom peptides ranging from evolutionary relationships of predator and prey, biological actions on excitable tissues, potential application as pharmacological intervention in disease therapy, and as part of multiple experimental approaches towards an understanding of the atomistic characterization of ion channel structure. This review examines the historical perspective of the study of conotoxin peptides active on sodium channels gated by transmembrane voltage, which has led to recent advances in ion channel research made possible with the exploitation of the diversity of these marine toxins.
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Affiliation(s)
- James R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID 83209, USA
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6
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Geffeney SL, Cordingley JA, Mitchell K, Hanifin CT. In Silico Analysis of Tetrodotoxin Binding in Voltage-Gated Sodium Ion Channels from Toxin-Resistant Animal Lineages. Mar Drugs 2022; 20:md20110723. [PMID: 36422001 PMCID: PMC9698786 DOI: 10.3390/md20110723] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2022] [Revised: 11/11/2022] [Accepted: 11/15/2022] [Indexed: 11/21/2022] Open
Abstract
Multiple animal species have evolved resistance to the neurotoxin tetrodotoxin (TTX) through changes in voltage-gated sodium ion channels (VGSCs). Amino acid substitutions in TTX-resistant lineages appear to be positionally convergent with changes in homologous residues associated with reductions in TTX block. We used homology modeling coupled with docking simulations to test whether positionally convergent substitutions generate functional convergence at the level of TTX–channel interactions. We found little evidence that amino acids at convergent positions generated similar patterns among TTX-resistant animal lineages across several metrics, including number of polar contacts, polar contact position, and estimates of binding energy. Though binding energy values calculated for TTX docking were reduced for some TTX-resistant channels, not all TTX-resistant channels and not all of our analyses returned reduced binding energy values for TTX-resistant channels. Our results do not support a simple model of toxin resistance where a reduced number of bonds between TTX and the channel protein prevents blocking. Rather models that incorporate flexibility and movement of the protein overall may better describe how homologous substitutions in the channel cause changes in TTX block.
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7
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Lin YC, Lai YC, Lin TH, Yang YC, Kuo CC. Selective stabilization of the intermediate inactivated Na+ channel by the new-generation anticonvulsant rufinamide. Biochem Pharmacol 2022; 197:114928. [DOI: 10.1016/j.bcp.2022.114928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 01/13/2022] [Accepted: 01/13/2022] [Indexed: 11/27/2022]
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8
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Choudhury K, Kasimova MA, McComas S, Howard RJ, Delemotte L. An open state of a voltage-gated sodium channel involving a π-helix and conserved pore-facing asparagine. Biophys J 2022; 121:11-22. [PMID: 34890580 PMCID: PMC8758419 DOI: 10.1016/j.bpj.2021.12.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 11/26/2021] [Accepted: 12/06/2021] [Indexed: 01/07/2023] Open
Abstract
Voltage-gated sodium (Nav) channels play critical roles in propagating action potentials and otherwise manipulating ionic gradients in excitable cells. These channels open in response to membrane depolarization, selectively permeating sodium ions until rapidly inactivating. Structural characterization of the gating cycle in this channel family has proved challenging, particularly due to the transient nature of the open state. A structure from the bacterium Magnetococcus marinus Nav (NavMs) was initially proposed to be open, based on its pore diameter and voltage-sensor conformation. However, the functional annotation of this model, and the structural details of the open state, remain disputed. In this work, we used molecular modeling and simulations to test possible open-state models of NavMs. The full-length experimental structure, termed here the α-model, was consistently dehydrated at the activation gate, indicating an inability to conduct ions. Based on a spontaneous transition observed in extended simulations, and sequence/structure comparison to other Nav channels, we built an alternative π-model featuring a helix transition and the rotation of a conserved asparagine residue into the activation gate. Pore hydration, ion permeation, and state-dependent drug binding in this model were consistent with an open functional state. This work thus offers both a functional annotation of the full-length NavMs structure and a detailed model for a stable Nav open state, with potential conservation in diverse ion-channel families.
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Affiliation(s)
- Koushik Choudhury
- Science for Life Laboratory, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Marina A. Kasimova
- Science for Life Laboratory, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden
| | - Sarah McComas
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Rebecca J. Howard
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
| | - Lucie Delemotte
- Science for Life Laboratory, Department of Applied Physics, KTH Royal Institute of Technology, Solna, Sweden,Corresponding author
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9
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Guidelli R, Becucci L. Deterministic model of Ca v3.1 Ca 2+ channel and a proposed sequence of its conformations. Bioelectrochemistry 2020; 136:107618. [PMID: 32795940 DOI: 10.1016/j.bioelechem.2020.107618] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Revised: 06/29/2020] [Accepted: 07/21/2020] [Indexed: 10/23/2022]
Abstract
A family of current-time curves of T-type Cav3.1 Ca2+ channels available in the literature is simulated by a kinetic model differing from that used for the interpretation of all salient features of Na+ and Shaker K+ channels by the insertion of a multiplying factor expressing the difference between the working potential ϕ and the reversal potential ϕr. This deterministic model is also used to simulate experimental curves taken from the literature for steady-state 'fast inactivation' and for a gradual passage from fast to 'slow inactivation'. A depolarizing pulse induces fast or slow inactivation depending on whether it lasts 100-500 ms or about 1 min, and is believed to cause a collapse of the central pore near the selectivity filter (SF). A number of features of fast and slow inactivation of Cav3.1 Ca2+ channels are qualitatively interpreted on the basis of a sequence of conformational states. Briefly, the conformation responsible for 'fast inactivation' is assumed to have the activation gate open and the inactivation gate (i.e., the SF) inactive. Immediately after a depolarizing pulse, this conformation is inactive and requires a sufficiently long rest time at a far negative holding potential to recover from inactivation. 'Slow inactivation' is ascribed to a different conformation with the activation gate closed and the SF inactive.
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Affiliation(s)
- Rolando Guidelli
- Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy.
| | - Lucia Becucci
- 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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Denomme N, Hull JM, Mashour GA. Role of Voltage-Gated Sodium Channels in the Mechanism of Ether-Induced Unconsciousness. Pharmacol Rev 2019; 71:450-466. [PMID: 31471460 DOI: 10.1124/pr.118.016592] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Despite continuous clinical use for more than 170 years, the mechanism of general anesthetics has not been completely characterized. In this review, we focus on the role of voltage-gated sodium channels in the sedative-hypnotic actions of halogenated ethers, describing the history of anesthetic mechanisms research, the basic neurobiology and pharmacology of voltage-gated sodium channels, and the evidence for a mechanistic interaction between halogenated ethers and sodium channels in the induction of unconsciousness. We conclude with a more integrative perspective of how voltage-gated sodium channels might provide a critical link between molecular actions of the halogenated ethers and the more distributed network-level effects associated with the anesthetized state across species.
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Affiliation(s)
- Nicholas Denomme
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
| | - Jacob M Hull
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
| | - George A Mashour
- Departments of Pharmacology (N.D.) and Anesthesiology (G.A.M.), Center for Consciousness Science (N.D., G.A.M.), and Neuroscience Graduate Program (J.M.H., G.A.M.), University of Michigan, Ann Arbor, Michigan
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11
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Convergent and parallel evolution in a voltage-gated sodium channel underlies TTX-resistance in the Greater Blue-ringed Octopus: Hapalochlaena lunulata. Toxicon 2019; 170:77-84. [DOI: 10.1016/j.toxicon.2019.09.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 09/09/2019] [Accepted: 09/11/2019] [Indexed: 12/24/2022]
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12
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Guidelli R, Becucci L. Merging Shaker K+ channel electrophysiology with structural data by a nucleation and growth mechanism. Electrochim Acta 2019. [DOI: 10.1016/j.electacta.2019.01.183] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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13
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Structural basis for antiarrhythmic drug interactions with the human cardiac sodium channel. Proc Natl Acad Sci U S A 2019; 116:2945-2954. [PMID: 30728299 PMCID: PMC6386684 DOI: 10.1073/pnas.1817446116] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Voltage-gated sodium channels play a central role in cellular excitability and are key targets for drug development. Recent breakthroughs in high-resolution cryo-electron microscopy protein structure determination, Rosetta computational protein structure modeling, and multimicrosecond molecular dynamics simulations are empowering advances in structural biology to study the atomistic details of channel−drug interactions. We used Rosetta structural computational modeling and molecular dynamics simulations to study the interactions of antiarrhythmic and local anesthetic drugs with cardiac sodium channel. Our results provide crucial atomic-scale mechanistic insights into the channel–drug interactions, necessary for the rational design of novel modulators of the human cardiac sodium channel to be used for the treatment of cardiac arrhythmias. The human voltage-gated sodium channel, hNaV1.5, is responsible for the rapid upstroke of the cardiac action potential and is target for antiarrhythmic therapy. Despite the clinical relevance of hNaV1.5-targeting drugs, structure-based molecular mechanisms of promising or problematic drugs have not been investigated at atomic scale to inform drug design. Here, we used Rosetta structural modeling and docking as well as molecular dynamics simulations to study the interactions of antiarrhythmic and local anesthetic drugs with hNaV1.5. These calculations revealed several key drug binding sites formed within the pore lumen that can simultaneously accommodate up to two drug molecules. Molecular dynamics simulations identified a hydrophilic access pathway through the intracellular gate and a hydrophobic access pathway through a fenestration between DIII and DIV. Our results advance the understanding of molecular mechanisms of antiarrhythmic and local anesthetic drug interactions with hNaV1.5 and will be useful for rational design of novel therapeutics.
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14
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Zhang XC, Li H. Interplay between the electrostatic membrane potential and conformational changes in membrane proteins. Protein Sci 2019; 28:502-512. [PMID: 30549351 DOI: 10.1002/pro.3563] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 12/12/2018] [Accepted: 12/13/2018] [Indexed: 12/16/2022]
Abstract
Transmembrane electrostatic membrane potential is a major energy source of the cell. Importantly, it determines the structure as well as function of charge-carrying membrane proteins. Here, we discuss the relationship between membrane potential and membrane proteins, in particular whether the conformation of these proteins is integrally connected to the membrane potential. Together, these concepts provide a framework for rationalizing the types of conformational changes that have been observed in membrane proteins and for better understanding the electrostatic effects of the membrane potential on both reversible as well as unidirectional dynamic processes of membrane proteins.
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Affiliation(s)
- Xuejun C Zhang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Hang Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
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15
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Modeling squid axon Na + channel by a nucleation and growth kinetic mechanism. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1861:100-109. [PMID: 30463693 DOI: 10.1016/j.bbamem.2018.08.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 08/02/2018] [Accepted: 08/19/2018] [Indexed: 11/21/2022]
Abstract
A kinetic model accounting for all salient features of the Na+ channel of the squid giant axon is provided. The model furnishes explanations for the Cole-Moore-like effect, the rising phase of the ON gating current and the slow 'intermediate component' of its decaying phase, as well as the gating charge immobilization. Experimental ON ionic currents are semi-quantitatively simulated by the use of only three free parameters, upon assuming that the Na+ channel opening proceeds along with the stepwise aggregation of its four domains, while they are moving their gating charge outward under depolarizing conditions. The inactivation phase of the ON ionic current is interpreted by a progressive electrostatic attraction between the positively charged 'hinged lid' containing the hydrophobic IFM triad and its receptor inside the channel pore, as the stepwise outward movement of the S4 segments of the Na+ channel progressively increases the negative charge attracting the triad to its receptor. The Na+ channel closing is assumed to proceed by repolarization-induced disaggregation of its domains, accompanied by inward movement of their gating charge. The phenomenon of 'gating charge immobilization' can be explained by assuming that gradual structural changes of the receptor over the time course of depolarization strengthen the interaction between the IFM triad and its receptor, causing a slow release of the gating charge during the subsequent repolarization.
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16
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Abstract
Ion channels are essential for cellular signaling. Voltage-gated ion channels (VGICs) are the largest and most extensively studied superfamily of ion channels. They possess modular structural features such as voltage-sensing domains that encircle and form mechanical connections with the pore-forming domains. Such features are intimately related to their function in sensing and responding to changes in the membrane potential. In the present work, we discuss the thermodynamic mechanisms of the VGIC superfamily, including the two-state gating mechanism, sliding-rocking mechanism of the voltage sensor, subunit cooperation, lipid-infiltration mechanism of inactivation, and the relationship with their structural features.
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17
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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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18
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Shen H, Zhou Q, Pan X, Li Z, Wu J, Yan N. Structure of a eukaryotic voltage-gated sodium channel at near-atomic resolution. Science 2017; 355:science.aal4326. [PMID: 28183995 DOI: 10.1126/science.aal4326] [Citation(s) in RCA: 283] [Impact Index Per Article: 40.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2016] [Accepted: 01/31/2017] [Indexed: 01/09/2023]
Abstract
Voltage-gated sodium (Nav) channels are responsible for the initiation and propagation of action potentials. They are associated with a variety of channelopathies and are targeted by multiple pharmaceutical drugs and natural toxins. Here, we report the cryogenic electron microscopy structure of a putative Nav channel from American cockroach (designated NavPaS) at 3.8 angstrom resolution. The voltage-sensing domains (VSDs) of the four repeats exhibit distinct conformations. The entrance to the asymmetric selectivity filter vestibule is guarded by heavily glycosylated and disulfide bond-stabilized extracellular loops. On the cytoplasmic side, a conserved amino-terminal domain is placed below VSDI, and a carboxy-terminal domain binds to the III-IV linker. The structure of NavPaS establishes an important foundation for understanding function and disease mechanism of Nav and related voltage-gated calcium channels.
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Affiliation(s)
- Huaizong Shen
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China.,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China
| | - Qiang Zhou
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China.,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Xiaojing Pan
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China.,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China
| | - Zhangqiang Li
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China.,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Jianping Wu
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China.,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
| | - Nieng Yan
- State Key Laboratory of Membrane Biology, Tsinghua University, Beijing 100084, China. .,Beijing Advanced Innovation Center for Structural Biology, Tsinghua University, Beijing 100084, China.,Tsinghua-Peking Joint Center for Life Sciences, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
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19
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Gawali V, Todt H. Mechanism of Inactivation in Voltage-Gated Na+ Channels. CURRENT TOPICS IN MEMBRANES 2016; 78:409-50. [DOI: 10.1016/bs.ctm.2016.07.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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20
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Gudes S, Barkai O, Caspi Y, Katz B, Lev S, Binshtok AM. The role of slow and persistent TTX-resistant sodium currents in acute tumor necrosis factor-α-mediated increase in nociceptors excitability. J Neurophysiol 2015; 113:601-19. [PMID: 25355965 PMCID: PMC4297796 DOI: 10.1152/jn.00652.2014] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Accepted: 10/26/2014] [Indexed: 12/12/2022] Open
Abstract
Tetrodotoxin-resistant (TTX-r) sodium channels are key players in determining the input-output properties of peripheral nociceptive neurons. Changes in gating kinetics or in expression levels of these channels by proinflammatory mediators are likely to cause the hyperexcitability of nociceptive neurons and pain hypersensitivity observed during inflammation. Proinflammatory mediator, tumor necrosis factor-α (TNF-α), is secreted during inflammation and is associated with the early onset, as well as long-lasting, inflammation-mediated increase in excitability of peripheral nociceptive neurons. Here we studied the underlying mechanisms of the rapid component of TNF-α-mediated nociceptive hyperexcitability and acute pain hypersensitivity. We showed that TNF-α leads to rapid onset, cyclooxygenase-independent pain hypersensitivity in adult rats. Furthermore, TNF-α rapidly and substantially increases nociceptive excitability in vitro, by decreasing action potential threshold, increasing neuronal gain and decreasing accommodation. We extended on previous studies entailing p38 MAPK-dependent increase in TTX-r sodium currents by showing that TNF-α via p38 MAPK leads to increased availability of TTX-r sodium channels by partial relief of voltage dependence of their slow inactivation, thereby contributing to increase in neuronal gain. Moreover, we showed that TNF-α also in a p38 MAPK-dependent manner increases persistent TTX-r current by shifting the voltage dependence of activation to a hyperpolarized direction, thus producing an increase in inward current at functionally critical subthreshold voltages. Our results suggest that rapid modulation of the gating of TTX-r sodium channels plays a major role in the mediated nociceptive hyperexcitability of TNF-α during acute inflammation and may lead to development of effective treatments for inflammatory pain, without modulating the inflammation-induced healing processes.
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Affiliation(s)
- Sagi Gudes
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
| | - Omer Barkai
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
| | - Yaki Caspi
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
| | - Ben Katz
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
| | - Shaya Lev
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
| | - Alexander M Binshtok
- Department of Medical Neurobiology, Institute for Medical Research Israel-Canada, The Hebrew University Faculty of Medicine, Jerusalem, Israel; and The Edmond and Lily Safra Center for Brain Sciences, The Hebrew University, Jerusalem, Israel
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21
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Novak KR, Norman J, Mitchell JR, Pinter MJ, Rich MM. Sodium channel slow inactivation as a therapeutic target for myotonia congenita. Ann Neurol 2015; 77:320-32. [PMID: 25515836 DOI: 10.1002/ana.24331] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Revised: 12/01/2014] [Accepted: 12/07/2014] [Indexed: 01/21/2023]
Abstract
OBJECTIVE Patients with myotonia congenita have muscle hyperexcitability due to loss-of-function mutations in the chloride channel in skeletal muscle, which causes spontaneous firing of muscle action potentials (myotonia), producing muscle stiffness. In patients, muscle stiffness lessens with exercise, a change known as the warmup phenomenon. Our goal was to identify the mechanism underlying warmup and to use this information to guide development of novel therapy. METHODS To determine the mechanism underlying warmup, we used a recently discovered drug to eliminate muscle contraction, thus allowing prolonged intracellular recording from individual muscle fibers during induction of warmup in a mouse model of myotonia congenita. RESULTS Changes in action potentials suggested slow inactivation of sodium channels as an important contributor to warmup. These data suggested that enhancing slow inactivation of sodium channels might offer effective therapy for myotonia. Lacosamide and ranolazine enhance slow inactivation of sodium channels and are approved by the US Food and Drug Administration for other uses in patients. We compared the efficacy of both drugs to mexiletine, a sodium channel blocker currently used to treat myotonia. In vitro studies suggested that both lacosamide and ranolazine were superior to mexiletine. However, in vivo studies in a mouse model of myotonia congenita suggested that side effects could limit the efficacy of lacosamide. Ranolazine produced fewer side effects and was as effective as mexiletine at a dose that produced none of mexiletine's hypoexcitability side effects. INTERPRETATION We conclude that ranolazine has excellent therapeutic potential for treatment of patients with myotonia congenita.
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Affiliation(s)
- Kevin R Novak
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
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22
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Lukacs P, Gawali VS, Cervenka R, Ke S, Koenig X, Rubi L, Zarrabi T, Hilber K, Stary-Weinzinger A, Todt H. Exploring the structure of the voltage-gated Na+ channel by an engineered drug access pathway to the receptor site for local anesthetics. J Biol Chem 2014; 289:21770-81. [PMID: 24947510 DOI: 10.1074/jbc.m113.541763] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Despite the availability of several crystal structures of bacterial voltage-gated Na(+) channels, the structure of eukaryotic Na(+) channels is still undefined. We used predictions from available homology models and crystal structures to modulate an external access pathway for the membrane-impermeant local anesthetic derivative QX-222 into the internal vestibule of the mammalian rNaV1.4 channel. Potassium channel-based homology models predict amino acid Ile-1575 in domain IV segment 6 to be in close proximity to Lys-1237 of the domain III pore-loop selectivity filter. The mutation K1237E has been shown previously to increase the diameter of the selectivity filter. We found that an access pathway for external QX-222 created by mutations of Ile-1575 was abolished by the additional mutation K1237E, supporting the notion of a close spatial relationship between sites 1237 and 1575. Crystal structures of bacterial voltage-gated Na(+) channels predict that the side chain of rNaV1.4 Trp-1531 of the domain IV pore-loop projects into the space between domain IV segment 6 and domain III pore-loop and, therefore, should obstruct the putative external access pathway. Indeed, mutations W1531A and W1531G allowed for exceptionally rapid access of QX-222. In addition, W1531G created a second non-selective ion-conducting pore, bypassing the outer vestibule but probably merging into the internal vestibule, allowing for control by the activation gate. These data suggest a strong structural similarity between bacterial and eukaryotic voltage-gated Na(+) channels.
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Affiliation(s)
- Peter Lukacs
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Vaibhavkumar S Gawali
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Rene Cervenka
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Song Ke
- Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, UZA 2, A-1090 Vienna, Austria
| | - Xaver Koenig
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Lena Rubi
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Touran Zarrabi
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Karlheinz Hilber
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
| | - Anna Stary-Weinzinger
- Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, UZA 2, A-1090 Vienna, Austria
| | - Hannes Todt
- From the Department of Neurophysiology and Neuropharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria and
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23
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Goldschen-Ohm MP, Chanda B. Probing gating mechanisms of sodium channels using pore blockers. Handb Exp Pharmacol 2014; 221:183-201. [PMID: 24737237 DOI: 10.1007/978-3-642-41588-3_9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several classes of small molecules and peptides bind at the central pore of voltage-gated sodium channels either from the extracellular or intracellular side of the membrane and block ion conduction through the pore. Biophysical studies that shed light on the chemical nature, accessibility, and kinetics of binding of these naturally occurring and synthetic compounds reveal a wealth of information about how these channels gate. Here, we discuss insights into the structural underpinnings of gating of the channel pore and its coupling to the voltage sensors obtained from pore blockers including site 1 neurotoxins and local anesthetics.
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24
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Abstract
Voltage-gated sodium channels initiate action potentials in nerve, muscle and other excitable cells. Early physiological studies described sodium selectivity, voltage-dependent activation and fast inactivation, and developed conceptual models for sodium channel function. This review article follows the topics of my 2013 Sharpey-Schafer Prize Lecture and gives an overview of research using a combination of biochemical, molecular biological, physiological and structural biological approaches that have elucidated the structure and function of sodium channels at the atomic level. Structural models for voltage-dependent activation, sodium selectivity and conductance, drug block and both fast and slow inactivation are discussed. A perspective for the future envisions new advances in understanding the structural basis for sodium channel function and the opportunity for structure-based discovery of novel therapeutics.
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Affiliation(s)
- William A Catterall
- W. A. Catterall: Department of Pharmacology, Box 357280, University of Washington, Seattle, WA 98195-7280, USA.
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25
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Wu M, Ye N, Sengupta B, Zakon HH. A naturally occurring amino acid substitution in the voltage-dependent sodium channel selectivity filter affects channel gating. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2013; 199:829-42. [PMID: 23979192 DOI: 10.1007/s00359-013-0845-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 07/29/2013] [Accepted: 08/01/2013] [Indexed: 12/19/2022]
Abstract
The pore of sodium channels contains a selectivity filter made of 4 amino acids, D/E/K/A. In voltage sensitive sodium channel (Nav) channels from jellyfish to human the fourth amino acid is Ala. This Ala, when mutated to Asp, promotes slow inactivation. In some Nav channels of pufferfishes, the Ala is replaced with Gly. We studied the biophysical properties of an Ala-to-Gly substitution (A1529G) in rat Nav1.4 channel expressed in Xenopus oocytes alone or with a β1 subunit. The Ala-to-Gly substitution does not affect monovalent cation selectivity and positively shifts the voltage-dependent inactivation curve, although co-expression with a β1 subunit eliminates the difference between A1529G and WT. There is almost no difference in channel fast inactivation, but the β1 subunit accelerates WT current inactivation significantly more than it does the A1529G channels. The Ala-to-Gly substitution mainly influences the rate of recovery from slow inactivation. Again, the β1 subunit is less effective on speeding recovery of A1529G than the WT. We searched Nav channels in numerous databases and noted at least four other independent Ala-to-Gly substitutions in Nav channels in teleost fishes. Thus, the Ala-to-Gly substitution occurs more frequently than previously realized, possibly under selection for alterations of channel gating.
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Affiliation(s)
- Mingming Wu
- Section of Neurobiology, Institute for Neuroscience, University of Texas at Austin, Austin, TX, 78712, USA,
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26
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Huang CJ, Schild L, Moczydlowski EG. Use-dependent block of the voltage-gated Na(+) channel by tetrodotoxin and saxitoxin: effect of pore mutations that change ionic selectivity. ACTA ACUST UNITED AC 2013; 140:435-54. [PMID: 23008436 PMCID: PMC3457692 DOI: 10.1085/jgp.201210853] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated Na(+) channels (NaV channels) are specifically blocked by guanidinium toxins such as tetrodotoxin (TTX) and saxitoxin (STX) with nanomolar to micromolar affinity depending on key amino acid substitutions in the outer vestibule of the channel that vary with NaV gene isoforms. All NaV channels that have been studied exhibit a use-dependent enhancement of TTX/STX affinity when the channel is stimulated with brief repetitive voltage depolarizations from a hyperpolarized starting voltage. Two models have been proposed to explain the mechanism of TTX/STX use dependence: a conformational mechanism and a trapped ion mechanism. In this study, we used selectivity filter mutations (K1237R, K1237A, and K1237H) of the rat muscle NaV1.4 channel that are known to alter ionic selectivity and Ca(2+) permeability to test the trapped ion mechanism, which attributes use-dependent enhancement of toxin affinity to electrostatic repulsion between the bound toxin and Ca(2+) or Na(+) ions trapped inside the channel vestibule in the closed state. Our results indicate that TTX/STX use dependence is not relieved by mutations that enhance Ca(2+) permeability, suggesting that ion-toxin repulsion is not the primary factor that determines use dependence. Evidence now favors the idea that TTX/STX use dependence arises from conformational coupling of the voltage sensor domain or domains with residues in the toxin-binding site that are also involved in slow inactivation.
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27
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Jones DK, Peters CH, Allard CR, Claydon TW, Ruben PC. Proton sensors in the pore domain of the cardiac voltage-gated sodium channel. J Biol Chem 2013; 288:4782-91. [PMID: 23283979 DOI: 10.1074/jbc.m112.434266] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Protons impart isoform-specific modulation of inactivation in neuronal, skeletal muscle, and cardiac voltage-gated sodium (Na(V)) channels. Although the structural basis of proton block in Na(V) channels has been well described, the amino acid residues responsible for the changes in Na(V) kinetics during extracellular acidosis are as yet unknown. We expressed wild-type (WT) and two pore mutant constructs (H880Q and C373F) of the human cardiac Na(V) channel, Na(V)1.5, in Xenopus oocytes. C373F and H880Q both attenuated proton block, abolished proton modulation of use-dependent inactivation, and altered pH modulation of the steady-state and kinetic parameters of slow inactivation. Additionally, C373F significantly reduced the maximum probability of use-dependent inactivation and slow inactivation, relative to WT. H880Q also significantly reduced the maximum probability of slow inactivation and shifted the voltage dependence of activation and fast inactivation to more positive potentials, relative to WT. These data suggest that Cys-373 and His-880 in Na(V)1.5 are proton sensors for use-dependent and slow inactivation and have implications in isoform-specific modulation of Na(V) channels.
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Affiliation(s)
- David K Jones
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
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28
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Zhang X, Ren W, DeCaen P, Yan C, Tao X, Tang L, Wang J, Hasegawa K, Kumasaka T, He J, Wang J, Clapham DE, Yan N. Crystal structure of an orthologue of the NaChBac voltage-gated sodium channel. Nature 2012; 486:130-4. [PMID: 22678295 DOI: 10.1038/nature11054] [Citation(s) in RCA: 362] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Accepted: 03/16/2012] [Indexed: 01/04/2023]
Abstract
Voltage-gated sodium (Na(v)) channels are essential for the rapid depolarization of nerve and muscle, and are important drug targets. Determination of the structures of Na(v) channels will shed light on ion channel mechanisms and facilitate potential clinical applications. A family of bacterial Na(v) channels, exemplified by the Na(+)-selective channel of bacteria (NaChBac), provides a useful model system for structure-function analysis. Here we report the crystal structure of Na(v)Rh, a NaChBac orthologue from the marine alphaproteobacterium HIMB114 (Rickettsiales sp. HIMB114; denoted Rh), at 3.05 Å resolution. The channel comprises an asymmetric tetramer. The carbonyl oxygen atoms of Thr 178 and Leu 179 constitute an inner site within the selectivity filter where a hydrated Ca(2+) resides in the crystal structure. The outer mouth of the Na(+) selectivity filter, defined by Ser 181 and Glu 183, is closed, as is the activation gate at the intracellular side of the pore. The voltage sensors adopt a depolarized conformation in which all the gating charges are exposed to the extracellular environment. We propose that Na(v)Rh is in an 'inactivated' conformation. Comparison of Na(v)Rh with Na(v)Ab reveals considerable conformational rearrangements that may underlie the electromechanical coupling mechanism of voltage-gated channels.
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Affiliation(s)
- Xu Zhang
- State Key Laboratory of Bio-membrane and Membrane Biotechnology, Center for Structural Biology, Tsinghua University, Beijing 100084, China
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29
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Capes DL, Arcisio-Miranda M, Jarecki BW, French RJ, Chanda B. Gating transitions in the selectivity filter region of a sodium channel are coupled to the domain IV voltage sensor. Proc Natl Acad Sci U S A 2012; 109:2648-53. [PMID: 22308389 PMCID: PMC3289344 DOI: 10.1073/pnas.1210413109] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2024] Open
Abstract
Voltage-dependent ion channels are crucial for generation and propagation of electrical activity in biological systems. The primary mechanism for voltage transduction in these proteins involves the movement of a voltage-sensing domain (D), which opens a gate located on the cytoplasmic side. A distinct conformational change in the selectivity filter near the extracellular side has been implicated in slow inactivation gating, which is important for spike frequency adaptation in neural circuits. However, it remains an open question whether gating transitions in the selectivity filter region are also actuated by voltage sensors. Here, we examine conformational coupling between each of the four voltage sensors and the outer pore of a eukaryotic voltage-dependent sodium channel. The voltage sensors of these sodium channels are not structurally symmetric and exhibit functional specialization. To track the conformational rearrangements of individual voltage-sensing domains, we recorded domain-specific gating pore currents. Our data show that, of the four voltage sensors, only the domain IV voltage sensor is coupled to the conformation of the selectivity filter region of the sodium channel. Trapping the outer pore in a particular conformation with a high-affinity toxin or disulphide crossbridge impedes the return of this voltage sensor to its resting conformation. Our findings directly establish that, in addition to the canonical electromechanical coupling between voltage sensor and inner pore gates of a sodium channel, gating transitions in the selectivity filter region are also coupled to the movement of a voltage sensor. Furthermore, our results also imply that the voltage sensor of domain IV is unique in this linkage and in the ability to initiate slow inactivation in sodium channels.
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Affiliation(s)
- Deborah L. Capes
- Department of Neuroscience, University of Wisconsin, Madison, WI 53706
- Molecular and Cellular Pharmacology Graduate Program, and
| | - Manoel Arcisio-Miranda
- Department of Neuroscience, University of Wisconsin, Madison, WI 53706
- Department of Biophysics, Federal University of Sao Paulo, 04023-060, Sao Paulo, Brazil; and
| | - Brian W. Jarecki
- Department of Neuroscience, University of Wisconsin, Madison, WI 53706
| | - Robert J. French
- Department of Physiology and Pharmacology, University of Calgary, Calgary, AB, Canada T2N 4N1
| | - Baron Chanda
- Department of Neuroscience, University of Wisconsin, Madison, WI 53706
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30
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Gating transitions in the selectivity filter region of a sodium channel are coupled to the domain IV voltage sensor. Proc Natl Acad Sci U S A 2012. [PMID: 22308389 DOI: 10.1073/pnas.1115575109] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-dependent ion channels are crucial for generation and propagation of electrical activity in biological systems. The primary mechanism for voltage transduction in these proteins involves the movement of a voltage-sensing domain (D), which opens a gate located on the cytoplasmic side. A distinct conformational change in the selectivity filter near the extracellular side has been implicated in slow inactivation gating, which is important for spike frequency adaptation in neural circuits. However, it remains an open question whether gating transitions in the selectivity filter region are also actuated by voltage sensors. Here, we examine conformational coupling between each of the four voltage sensors and the outer pore of a eukaryotic voltage-dependent sodium channel. The voltage sensors of these sodium channels are not structurally symmetric and exhibit functional specialization. To track the conformational rearrangements of individual voltage-sensing domains, we recorded domain-specific gating pore currents. Our data show that, of the four voltage sensors, only the domain IV voltage sensor is coupled to the conformation of the selectivity filter region of the sodium channel. Trapping the outer pore in a particular conformation with a high-affinity toxin or disulphide crossbridge impedes the return of this voltage sensor to its resting conformation. Our findings directly establish that, in addition to the canonical electromechanical coupling between voltage sensor and inner pore gates of a sodium channel, gating transitions in the selectivity filter region are also coupled to the movement of a voltage sensor. Furthermore, our results also imply that the voltage sensor of domain IV is unique in this linkage and in the ability to initiate slow inactivation in sodium channels.
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31
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Iravanian S, Lloyd MS, Langberg JJ. Left atrial flutter accelerates during ablation of atrial fibrillation: a paradoxical effect of electrical remodelling. Europace 2011; 14:761-6. [PMID: 22183745 DOI: 10.1093/europace/eur385] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS Atrial fibrillation (AF)-induced electrical remodelling causes shortening of refractory period and slowing of conduction velocity. During the course of catheter ablation of AF, there are often transitions from AF to left atrial flutter (AFL) and from faster to slower AFL. The purpose of this study was to characterize the time course of change in AFL rate during AF ablation. METHODS AND RESULTS Fourier transformation was performed on 16 s segments of coronary sinus and ablation catheter bipolar electrograms. Ablation-induced AF-to-AFL and AFL-to-AFL transitions were defined as a sudden drop in the dominant frequency (DF) of at least 10 bpm, followed by a regular rhythm. Forty-five transitions were detected in 24 ablation procedures. The mean DF in AF was 5.31 ± 0.79 Hz, which was significantly faster than AFL, 4.52 ± 0.62 Hz (P< 0.05). The mean ΔDF at transitions was -51 ± 16 bpm in AF and -40 ± 14 bpm in AFL. Dominant frequency slope was positive (rate increased) after all the transitions during AF (P< 0.0001) and in 11 of 14 transitions in AFL (P= 0.033). The time constant of the DF recovery curve was 161 ± 105 s. CONCLUSIONS After ablation-induced transition from AF to AFL, or faster to slower AFL, there is a progressive increase in AFL rate over time. The mechanism of this acceleration is uncertain, but the time constant of this rate increase is consistent with the recovery of the slow/ultraslow sodium current in the setting of established electrical remodelling.
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32
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Bett GCL, Dinga-Madou I, Zhou Q, Bondarenko VE, Rasmusson RL. A model of the interaction between N-type and C-type inactivation in Kv1.4 channels. Biophys J 2011; 100:11-21. [PMID: 21190652 DOI: 10.1016/j.bpj.2010.11.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 09/24/2010] [Accepted: 11/08/2010] [Indexed: 01/12/2023] Open
Abstract
Kv1.4 channels are Shaker-related voltage-gated potassium channels with two distinct inactivation mechanisms. Fast N-type inactivation operates by a ball-and-chain mechanism. Slower C-type inactivation is not so well defined, but involves intracellular and extracellular conformational changes of the channel. We studied the interaction between inactivation mechanisms using two-electrode voltage-clamp of Kv1.4 and Kv1.4ΔN (amino acids 2-146 deleted to remove N-type inactivation) heterologously expressed in Xenopus oocytes. We manipulated C-type inactivation by introducing a lysine-tyrosine point mutation (K532Y, equivalent to Shaker T449Y) that diminishes C-type inactivation. We used experimental data to develop a comprehensive computer model of Kv1.4 channels to determine the interaction between activation and N- and C-type inactivation mechanisms needed to replicate the experimental data. C-type inactivation began at lower voltage preactivated states, whereas N-type inactivation was coupled directly to the open state. A model with distinct N- and C-type inactivated states was not able to reproduce experimental data, and direct transitions between N- and C-type inactivated states were required, i.e., there is coupling between N- and C-type inactivated states. C-type inactivation is the rate-limiting step determining recovery from inactivation, so understanding C-type inactivation, and how it is coupled to N-type inactivation, is critical in understanding how channels act to repetitive stimulation.
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Affiliation(s)
- Glenna C L Bett
- Department of Gynecology-Obstetrics, The State University of New York, University at Buffalo, Buffalo, New York, USA
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33
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Zarrabi T, Cervenka R, Sandtner W, Lukacs P, Koenig X, Hilber K, Mille M, Lipkind GM, Fozzard HA, Todt H. A molecular switch between the outer and the inner vestibules of the voltage-gated Na+ channel. J Biol Chem 2010; 285:39458-70. [PMID: 20926383 PMCID: PMC2998134 DOI: 10.1074/jbc.m110.132886] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Voltage-gated ion channels are transmembrane proteins that undergo complex conformational changes during their gating transitions. Both functional and structural data from K+ channels suggest that extracellular and intracellular parts of the pore communicate with each other via a trajectory of interacting amino acids. No crystal structures are available for voltage-gated Na+ channels, but functional data suggest a similar intramolecular communication involving the inner and outer vestibules. However, the mechanism of such communication is unknown. Here, we report that amino acid Ile-1575 in the middle of transmembrane segment 6 of domain IV (DIV-S6) in the adult rat skeletal muscle isoform of the voltage-gated sodium channel (rNaV1.4) may act as molecular switch allowing for interaction between outer and inner vestibules. Cysteine scanning mutagenesis of the internal part of DIV-S6 revealed that only mutations at site 1575 rescued the channel from a unique kinetic state (“ultra-slow inactivation,” IUS) produced by the mutation K1237E in the selectivity filter. A similar effect was seen with I1575A. Previously, we reported that conformational changes of both the internal and the external vestibule are involved in the generation of IUS. The fact that mutations at site 1575 modulate IUS produced by K1237E strongly suggests an interaction between these sites. Our data confirm a previously published molecular model in which Ile-1575 of DIV-S6 is in close proximity to Lys-1237 of the selectivity filter. Furthermore, these functional data define the position of the selectivity filter relative to the adjacent DIV-S6 segment within the ionic permeation pathway.
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Affiliation(s)
- Touran Zarrabi
- Center for Physiology and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna 1090, Austria
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34
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Biophysical costs associated with tetrodotoxin resistance in the sodium channel pore of the garter snake, Thamnophis sirtalis. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2010; 197:33-43. [PMID: 20820785 DOI: 10.1007/s00359-010-0582-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 08/24/2010] [Accepted: 08/25/2010] [Indexed: 12/19/2022]
Abstract
Tetrodotoxin (TTX) is a potent toxin that specifically binds to voltage-gated sodium channels (NaV). TTX binding physically blocks the flow of sodium ions through NaV, thereby preventing action potential generation and propagation. TTX has different binding affinities for different NaV isoforms. These differences are imparted by amino acid substitutions in positions within, or proximal to, the TTX-binding site in the channel pore. These substitutions confer TTX-resistance to a variety of species. The garter snake Thamnophis sirtalis has evolved TTX-resistance over the course of an arms race, allowing some populations of snakes to feed on tetrodotoxic newts, including Taricha granulosa. Different populations of the garter snake have different degrees of TTX-resistance, which is closely related to the number of amino acid substitutions. We tested the biophysical properties and ion selectivity of NaV of three garter snake populations from Bear Lake, Idaho; Warrenton, Oregon; and Willow Creek, California. We observed changes in gating properties of TTX-resistant (TTXr) NaV. In addition, ion selectivity of TTXr NaV was significantly different from that of TTX-sensitive NaV. These results suggest TTX-resistance comes at a cost to performance caused by changes in the biophysical properties and ion selectivity of TTXr NaV.
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35
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Cervenka R, Zarrabi T, Lukacs P, Todt H. The outer vestibule of the Na+ channel-toxin receptor and modulator of permeation as well as gating. Mar Drugs 2010; 8:1373-93. [PMID: 20479982 PMCID: PMC2866490 DOI: 10.3390/md8041373] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 03/31/2010] [Accepted: 04/19/2010] [Indexed: 12/19/2022] Open
Abstract
The outer vestibule of voltage-gated Na(+) channels is formed by extracellular loops connecting the S5 and S6 segments of all four domains ("P-loops"), which fold back into the membrane. Classically, this structure has been implicated in the control of ion permeation and in toxin blockage. However, conformational changes of the outer vestibule may also result in alterations in gating, as suggested by several P-loop mutations that gave rise to gating changes. Moreover, partial pore block by mutated toxins may reverse gating changes induced by mutations. Therefore, toxins that bind to the outer vestibule can be used to modulate channel gating.
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Affiliation(s)
| | | | - Peter Lukacs
- Institute of Pharmacology, Centre of Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria; E-Mails:
(R.C.);
(T.Z.);
(P.L.)
| | - Hannes Todt
- Institute of Pharmacology, Centre of Physiology and Pharmacology, Medical University of Vienna, 1090 Vienna, Austria; E-Mails:
(R.C.);
(T.Z.);
(P.L.)
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36
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Yamagishi T, Xiong W, Kondratiev A, Vélez P, Méndez-Fitzwilliam A, Balser JR, Marbán E, Tomaselli GF. Novel molecular determinants in the pore region of sodium channels regulate local anesthetic binding. Mol Pharmacol 2009; 76:861-71. [PMID: 19620257 DOI: 10.1124/mol.109.055863] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
The pore of the Na+ channel is lined by asymmetric loops formed by the linkers between the fifth and sixth transmembrane segments (S5-S6). We investigated the role of the N-terminal portion (SS1) of the S5-S6 linkers in channel gating and local anesthetic (LA) block using site-directed cysteine mutagenesis of the rat skeletal muscle (Na(V)1.4) channel. The mutants examined have variable effects on voltage dependence and kinetics of fast inactivation. Of the cysteine mutants immediately N-terminal to the putative DEKA selectivity filter in four domains, only Q399C in domain I and F1236C in domain III exhibit reduced use-dependent block. These two mutations also markedly accelerated the recovery from use-dependent block. Moreover, F1236C and Q399C significantly decreased the affinity of QX-314 for binding to its channel receptor by 8.5- and 3.3-fold, respectively. Oddly enough, F1236C enhanced stabilization of slow inactivation by both hastening entry into and delaying recovery from slow inactivation states. It is noteworthy that symmetric applications of QX-314 on both external and internal sides of F1236C mutant channels reduced recovery from use-dependent block, indicating an allosteric effect of external QX-314 binding on the recovery of availability of F1236C. These observations suggest that cysteine mutation in the SS1 region, particularly immediate adjacent to the DEKA ring, may lead to a structural rearrangement that alters binding of permanently charged QX-314 to its receptor. The results lend further support for a role for the selectivity filter region as a structural determinant for local anesthetic block.
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Affiliation(s)
- Toshio Yamagishi
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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37
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Filatov GN, Pinter MJ, Rich MM. Role of Ca(2+) in injury-induced changes in sodium current in rat skeletal muscle. Am J Physiol Cell Physiol 2009; 297:C352-9. [PMID: 19494240 DOI: 10.1152/ajpcell.00021.2009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Characteristics of voltage-dependent sodium current recorded from adult rat muscle fibers in loose patch mode were rapidly altered following nearby impalement with a microelectrode. Hyperpolarized shifts in the voltage dependence of activation and fast inactivation occurred within minutes. In addition, the amplitude of the maximal sodium current decreased within 30 min of impalement. Impalement triggered a sustained elevation of intracellular Ca(2+). However, buffering Ca(2+) by loading fibers with AM-BAPTA did not affect the hyperpolarized shifts in activation and inactivation, although it did prevent the reduction in current amplitude. Surprisingly, the rise in intracellular Ca(2+) occurred even in the absence of extracellular Ca(2+). This result indicated that the injury-induced Ca(2+) increase came from an intracellular source, but it was not blocked by an inhibitor of release from the sarcoplasmic reticulum, which suggested involvement of mitochondria. Ca(2+) release from mitochondria triggered by carbonyl cyanide 3-chlorophenylhydrazone was sufficient to cause a reduction in sodium current amplitude but had little effect of the voltage dependence of activation and fast inactivation. Our data suggest the effects of muscle injury can be separated into a Ca(2+)-dependent reduction in amplitude and a largely Ca(2+)-independent shift in activation and fast inactivation. Together, the impalement-induced changes in sodium current reduce the number of sodium channels available to open at the resting potential and may limit further depolarization and thus promote survival of muscle fibers following injury.
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Affiliation(s)
- Gregory N Filatov
- Department of Cell Biology and Neuroscience, University of California, Riverside, CA, USA
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38
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Webb J, Wu FF, Cannon SC. Slow inactivation of the NaV1.4 sodium channel in mammalian cells is impeded by co-expression of the beta1 subunit. Pflugers Arch 2008; 457:1253-63. [PMID: 18941776 DOI: 10.1007/s00424-008-0600-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Accepted: 10/08/2008] [Indexed: 10/21/2022]
Abstract
In response to sustained depolarization or prolonged bursts of activity in spiking cells, sodium channels enter long-lived non-conducting states from which recovery at hyperpolarized potentials occurs over hundreds of milliseconds to seconds. The molecular basis for this slow inactivation remains unknown, although many functional domains of the channel have been implicated. Expression studies in Xenopus oocytes and mammalian cell lines have suggested a role for the accessory beta1 subunit in slow inactivation, but the effects have been variable. We examined the effects of the beta1 subunit on slow inactivation of skeletal muscle (NaV1.4) sodium channels expressed in HEK cells. Co-expression of the beta1 subunit impeded slow inactivation elicited by a 30-s depolarization, such that the voltage dependence was right shifted (depolarized) and recovery was hastened. Mutational studies showed this effect was dependent upon the extracellular Ig-like domain, but was independent of the intracellular C-terminal tail. Furthermore, the beta1 effect on slow inactivation was shown to be independent of the negative coupling between fast and slow inactivation.
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Affiliation(s)
- Jadon Webb
- Neuroscience Program, UT Southwestern Medical Center, Dallas, TX 75390, USA
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39
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Szendroedi J, Sandtner W, Zarrabi T, Zebedin E, Hilber K, Dudley SC, Fozzard HA, Todt H. Speeding the recovery from ultraslow inactivation of voltage-gated Na+ channels by metal ion binding to the selectivity filter: a foot-on-the-door? Biophys J 2007; 93:4209-24. [PMID: 17720727 PMCID: PMC2098733 DOI: 10.1529/biophysj.107.104794] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Slow inactivated states in voltage-gated ion channels can be modulated by binding molecules both to the outside and to the inside of the pore. Thus, external K(+) inhibits C-type inactivation in Shaker K(+) channels by a "foot-in-the-door" mechanism. Here, we explore the modulation of a very long-lived inactivated state, ultraslow inactivation (I(US)), by ligand binding to the outer vestibule in voltage-gated Na(+) channels. Blocking the outer vestibule by a mutant mu-conotoxin GIIIA substantially accelerated recovery from I(US). A similar effect was observed if Cd(2+) was bound to a cysteine engineered to the selectivity filter (K1237C). In K1237C channels, exposed to 30 microM Cd(2+), the time constant of recovery from I(US) was decreased from 145.0 +/- 10.2 s to 32.5 +/- 3.3 s (P < 0.001). Recovery from I(US) was only accelerated if Cd(2+) was added to the bath solution during recovery (V = -120 mV) from I(US), but not when the channels were selectively exposed to Cd(2+) during the development of I(US) (-20 mV). These data could be explained by a kinetic model in which Cd(2+) binds with high affinity to a slow inactivated state (I(S)), which is transiently occupied during recovery from I(US). A total of 50 microM Cd(2+) produced an approximately 8 mV hyperpolarizing shift of the steady-state inactivation curve of I(S), supporting this kinetic model. Binding of lidocaine to the internal vestibule significantly reduced the number of channels entering I(US), suggesting that I(US) is associated with a conformational change of the internal vestibule of the channel. We propose a molecular model in which slow inactivation (I(S)) occurs by a closure of the outer vestibule, whereas I(US) arises from a constriction of the internal vestibule produced by a widening of the selectivity filter region. Binding of Cd(2+) to C1237 promotes the closure of the selectivity filter region, thereby hastening recovery from I(US). Thus, Cd(2+) ions may act like a foot-on-the-door, kicking the I(S) gate to close.
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Affiliation(s)
- Julia Szendroedi
- Center for Biomolecular Medicine and Pharmacology, Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
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40
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Tian L, Jiang X, Rasmusson R, Wang S. Effect of propafenone on Kv1.4 inactivation. J Physiol Biochem 2007; 62:263-70. [PMID: 17615952 DOI: 10.1007/bf03165755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Interactions between antiarrhythmic drugs and ion channels are important subjects in the field of cardiovascular electro-pharmacology. This study explores the relationship between propafenone and C-type inactivation of Kv1.4 channel. fKvl.4deltaN, a ferret Kv1.4 N-terminal deleted mutant, was employed in this study. fKvl.4deltaN cRNA was injected into Xenopus oocytes to express fKvl.4deltaN channel and two electrode voltage clamp technique was used to record the current. We found that fKvl.4deltaN channel current was rapidly depressed in a frequency-dependent manner and meanwhile, C-type inactivation in this channel was increased more than 7 folds in the presence of 100 microM propafenone. While propafenone has no effect on Kv1.4deltaN recovery. All the results indicate that propafenone blocks Kvl.4deltaN channel through intracellular bindings and that binding of propafenone with Kvl.4deltaN channel leads to a conformational change on the extracellular site which accelerates C-type inactivation, suggesting that propafenone, as an open channel blocker, may affect the mechanism of C-type inactivation.
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Affiliation(s)
- L Tian
- Department of Cardiology, Renmin Hospital of Wuhan University, 238 Jiefang Road, Wuhan, Hubei, China 430060
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41
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Thomas EA, Xu R, Petrou S. Computational analysis of the R85C and R85H epilepsy mutations in Na+ channel β1 subunits. Neuroscience 2007; 147:1034-46. [PMID: 17604911 DOI: 10.1016/j.neuroscience.2007.05.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2006] [Revised: 05/11/2007] [Accepted: 05/14/2007] [Indexed: 12/30/2022]
Abstract
Mutations in Na+ channels cause a variety of epilepsy syndromes. Analysis of these mutations shows a range of simultaneous functional consequences, each of which may increase or decrease membrane excitability, making it difficult to predict the combined effect on neuron firing. This may be addressed by building mathematical models of Na+ channel gating and using them in neuron models to predict responses to natural stimuli. The R85C and R85H mutations of the beta1 subunit cause generalized epilepsy syndromes in humans, and an experimental study showed that these mutations shift steady-state activation in the negative direction, which predicts increased excitability, and shift fast inactivation in the negative direction, which predicts decreased excitability. In addition, the R85C also shifts slow inactivation in the negative direction. To predict changes in neuron excitability resulting from these contradictory effects we built Na+ channel models based on our earlier data and on new measurements of the rate of slow inactivation over a range of potentials. Use of these Na+ channel models in simple neuron models revealed that both mutations cause an increase in excitability but the R85H mutation was more excitable. This is due to differences in steady-state slow inactivation and to subtle differences in fast kinetics captured by the model fitting process. To understand the effect of changes in different gating processes and to provide a simple guide for interpreting changes caused by mutations, we performed a sensitivity analysis. Using the wild-type model we shifted each activation curve by +/-5 mV or altered gating rates up or down by 20%. Excitability was most sensitive to changes in voltage dependence of activation, followed by voltage dependence of inactivation and then slow inactivation. By contrast, excitability was relatively insensitive to gating rates.
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Affiliation(s)
- E A Thomas
- Howard Florey Institute, University of Melbourne, Parkville 3010, Australia
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42
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Tikhonov DB, Zhorov BS. Sodium channels: ionic model of slow inactivation and state-dependent drug binding. Biophys J 2007; 93:1557-70. [PMID: 17496040 PMCID: PMC1948041 DOI: 10.1529/biophysj.106.100248] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Inactivation is a fundamental property of voltage-gated ion channels. Fast inactivation of Na(+) channels involves channel block by the III-IV cytoplasmic interdomain linker. The mechanisms of nonfast types of inactivation (intermediate, slow, and ultraslow) are unclear, although the ionic environment and P-loops rearrangement appear to be involved. In this study, we employed a TTX-based P-loop domain model of a sodium channel and the MCM method to investigate a possible role of P-loop rearrangement in the nonfast inactivation. Our modeling predicts that Na(+) ions can bind between neighboring domains in the outer-carboxylates ring EEDD, forming an ordered structure with interdomain contacts that stabilize the conducting conformation of the outer pore. In this model, the permeant ions can transit between the EEDD ring and the selectivity filter ring DEKA, retaining contacts with at least two carboxylates. In the absence of Na(+), the electrostatic repulsion between the EEDD carboxylates disrupts the permeable configuration. In this Na(+)-deficient model, the region between the EEDD and DEKA rings is inaccessible for Na(+) but is accessible for TMA. Taken together, these results suggest that Na(+)-saturated models are consistent with experimental characteristics of the open channels, whereas Na(+)-deficient models are consistent with experimentally defined properties of the slow-inactivated channels. Our calculations further predict that binding of LAs to the inner pore would depend on whether Na(+) occupies the DEKA ring. In the absence of Na(+) in the DEKA ring, the cationic group of lidocaine occurs in the focus of the pore helices' macrodipoles and would prevent occupation of the ring by Na(+). Loading the DEKA ring with Na(+) results in the electrostatic repulsion with lidocaine. Thus, there are antagonistic relations between a cationic ligand bound in the inner pore and Na(+) in the DEKA ring.
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Affiliation(s)
- Denis B Tikhonov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
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43
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Aman TK, Raman IM. Subunit dependence of Na channel slow inactivation and open channel block in cerebellar neurons. Biophys J 2006; 92:1938-51. [PMID: 17189307 PMCID: PMC1861793 DOI: 10.1529/biophysj.106.093500] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Purkinje and cerebellar nuclear neurons both have Na currents with resurgent kinetics. Previous observations, however, suggest that their Na channels differ in their susceptibility to entering long-lived inactivated states. To compare fast inactivation, slow inactivation, and open-channel block, we recorded voltage-clamped, tetrodotoxin-sensitive Na currents in Purkinje and nuclear neurons acutely isolated from mouse cerebellum. In nuclear neurons, recovery from all inactivated states was slower, and open-channel unblock was less voltage-dependent than in Purkinje cells. To test whether specific subunits contributed to this differential stability of inactivation, experiments were repeated in Na(V)1.6-null (med) mice. In med Purkinje cells, recovery times were prolonged and the voltage dependence of open-channel block was reduced relative to control cells, suggesting that availability of Na(V)1.6 is quickly restored at negative potentials. In med nuclear cells, however, currents were unchanged, suggesting that Na(V)1.6 contributes little to wild-type nuclear cells. Extracellular Na(+) prevented slow inactivation more effectively in Purkinje than in nuclear neurons, consistent with a resilience of Na(V)1.6 to slow inactivation. The tendency of nuclear Na channels to inactivate produced a low availability during trains of spike-like depolarization. Hyperpolarizations that approximated synaptic inhibition effectively recovered channels, suggesting that increases in Na channel availability promote rebound firing after inhibition.
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Affiliation(s)
- Teresa K Aman
- Interdepartmental Neuroscience Program and Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA
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44
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Pfahnl AE, Viswanathan PC, Weiss R, Shang LL, Sanyal S, Shusterman V, Kornblit C, London B, Dudley SC. A sodium channel pore mutation causing Brugada syndrome. Heart Rhythm 2006; 4:46-53. [PMID: 17198989 PMCID: PMC1779366 DOI: 10.1016/j.hrthm.2006.09.031] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2006] [Accepted: 09/27/2006] [Indexed: 01/08/2023]
Abstract
BACKGROUND Brugada and long QT type 3 syndromes are linked to sodium channel mutations and clinically cause arrhythmias that lead to sudden death. We have identified a novel threonine-to-isoleucine missense mutation at position 353 (T353I) adjacent to the pore-lining region of domain I of the cardiac sodium channel (SCN5A) in a family with Brugada syndrome. Both male and female carriers are symptomatic at young ages, have typical Brugada-type electrocardiogram changes, and have relatively normal corrected QT intervals. OBJECTIVES To characterize the properties of the newly identified cardiac sodium channel (SCN5A) mutation at the cellular level. RESULTS Using whole-cell voltage clamp, we found that heterologous expression of SCN5A containing the T353I mutation resulted in 74% +/- 6% less peak macroscopic sodium current when compared with wild-type channels. A construct of the T353I mutant channel fused with green fluorescent protein failed to traffic properly to the sarcolemma, with a large proportion of channels sequestered intracellularly. Overnight exposure to 0.1 mM mexiletine, a Na(+) channel blocking agent, increased T353I channel trafficking to the membrane to near normal levels, but the mutant channels showed a significant late current that was 1.6% +/- 0.2% of peak sodium current at 200 ms, a finding seen with long QT mutations. CONCLUSIONS The clinical presentation of patients carrying the T353I mutation is that of Brugada syndrome and could be explained by a cardiac Na(+) channel trafficking defect. However, when the defect was ameliorated, the mutated channels had biophysical properties consistent with long QT syndrome. The lack of phenotypic changes associated with the long QT syndrome could be explained by a T353I-induced trafficking defect reducing the number of mutant channels with persistent currents present at the sarcolemma.
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Affiliation(s)
- Arnold E. Pfahnl
- Division of Cardiology, Atlanta Veterans Affairs Medical Center and Emory University, Atlanta, GA, 30033
| | | | | | - Lijuan L. Shang
- Division of Cardiology, Atlanta Veterans Affairs Medical Center and Emory University, Atlanta, GA, 30033
| | - Shamrendra Sanyal
- Division of Cardiology, Atlanta Veterans Affairs Medical Center and Emory University, Atlanta, GA, 30033
| | | | - Cari Kornblit
- Cardiovascular Institute, University of Pittsburgh, Pittsburgh, PA 15213
| | - Barry London
- Cardiovascular Institute, University of Pittsburgh, Pittsburgh, PA 15213
| | - Samuel C. Dudley
- Division of Cardiology, Atlanta Veterans Affairs Medical Center and Emory University, Atlanta, GA, 30033
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45
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Xiong W, Farukhi YZ, Tian Y, Disilvestre D, Li RA, Tomaselli GF. A conserved ring of charge in mammalian Na+ channels: a molecular regulator of the outer pore conformation during slow inactivation. J Physiol 2006; 576:739-54. [PMID: 16873407 PMCID: PMC1890405 DOI: 10.1113/jphysiol.2006.115105] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The molecular mechanisms underlying slow inactivation in sodium channels are elusive. Our results suggest that EEDD, a highly conserved ring of charge in the external vestibule of mammalian voltage-gated sodium channels, undermines slow inactivation. By employing site-directed mutagenesis, we found that charge alterations in this asymmetric yet strong local electrostatic field of the EEDD ring significantly altered the kinetics of slow inactivation gating. Using a non-linear Poisson-Boltzmann equation, quantitative computations of the electrostatic field in a sodium channel structural model suggested a significant electrostatic repulsion between residues E403 and E758 at close proximity. Interestingly, when this electrostatic interaction was eliminated by the double mutation E403C + E758C, the kinetics of recovery from slow inactivation of the double-mutant channel was retarded by 2500% compared to control. These data suggest that the EEDD ring, located within the asymmetric electric field, is a molecular motif that critically modulates slow inactivation in sodium channels.
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Affiliation(s)
- Wei Xiong
- Department of Medicine, Johns Hopkins University School of Medicine, 720 Rutland Ave/Ross 844, Baltimore, MD 21205, USA
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47
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Marine Toxins That Target Voltage-gated Sodium Channels. Mar Drugs 2006. [PMCID: PMC3663416] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Eukaryotic, voltage-gated sodium (NaV) channels are large membrane proteins which underlie generation and propagation of rapid electrical signals in nerve, muscle and heart. Nine different NaV receptor sites, for natural ligands and/or drugs, have been identified, based on functional analyses and site-directed mutagenesis. In the marine ecosystem, numerous toxins have evolved to disrupt NaV channel function, either by inhibition of current flow through the channels, or by modifying the activation and inactivation gating processes by which the channels open and close. These toxins function in their native environment as offensive or defensive weapons in prey capture or deterrence of predators. In composition, they range from organic molecules of varying size and complexity to peptides consisting of ~10–70 amino acids. We review the variety of known NaV-targeted marine toxins, outlining, where known, their sites of interaction with the channel protein and their functional effects. In a number of cases, these natural ligands have the potential applications as drugs in clinical settings, or as models for drug development.
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Hilber K, Sandtner W, Zarrabi T, Zebedin E, Kudlacek O, Fozzard HA, Todt H. Selectivity filter residues contribute unequally to pore stabilization in voltage-gated sodium channels. Biochemistry 2006; 44:13874-82. [PMID: 16229476 DOI: 10.1021/bi0511944] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mutations in the putative selectivity filter region of the voltage-gated Na+ channel, the so-called DEKA-motif, not only affect selectivity but also alter the channel's gating properties, suggesting functional coupling between permeation and gating. We have previously reported that charge-altering mutations at position 1237 in the P-loop of domain III (position K of the DEKA-motif in the adult rat skeletal muscle Na+ channel, rNa(v)1.4) dramatically enhanced entry to an inactivated state from which the channels recovered with a very slow time constant on the order of approximately 100 s (Todt, H., Dudley, S. C. J., Kyle, J. W., French, R. J., and Fozzard, H. A. (1999) Biophys. J. 76, 1335-1345). This state, termed "ultra-slow inactivation", may reflect a complex molecular rearrangement of the channel's pore region that involves both the extracellular and the cytoplasmic pore. Here, we tested whether charged DEKA-motif residues other than K1237 were also important determinants of a channel's gating properties. Therefore, we constructed the charge-neutralizing mutations D400A, E755A, and K1237A and studied the effects of these mutations on I(US). We found that, compared to wild-type rNa(v)1.4 channels, mutant D400A and K1237A but not E755A channels exhibited enhanced entry into ultra-slow inactivation. Selectivity for Na+ over K+, as judged from shifts in reversal potentials, was preserved in D400A, reduced in E755A, and completely lost in K1237A. These data suggest that an electrostatic interaction between the positively charged residue K1237 and the negatively charged residue D400 stabilizes the structure of the pore and thereby prevents I(US). Moreover, the interaction between K1237 and E755 appears to provide the basis for selective permeation of Na+ over K+.
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Affiliation(s)
- Karlheinz Hilber
- Center of Biomolecular Medicine and Pharmacology, Medical University of Vienna, Vienna, Austria
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Chen Y, Yu FH, Surmeier DJ, Scheuer T, Catterall WA. Neuromodulation of Na+ channel slow inactivation via cAMP-dependent protein kinase and protein kinase C. Neuron 2006; 49:409-20. [PMID: 16446144 DOI: 10.1016/j.neuron.2006.01.009] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Revised: 10/07/2005] [Accepted: 01/05/2006] [Indexed: 12/14/2022]
Abstract
Neurotransmitters modulate sodium channel availability through activation of G protein-coupled receptors, cAMP-dependent protein kinase (PKA), and protein kinase C (PKC). Voltage-dependent slow inactivation also controls sodium channel availability, synaptic integration, and neuronal firing. Here we show by analysis of sodium channel mutants that neuromodulation via PKA and PKC enhances intrinsic slow inactivation of sodium channels, making them unavailable for activation. Mutations in the S6 segment in domain III (N1466A,D) either enhance or block slow inactivation, implicating S6 segments in the molecular pathway for slow inactivation. Modulation of N1466A channels by PKC or PKA is increased, whereas modulation of N1466D is nearly completely blocked. These results demonstrate that neuromodulation by PKA and PKC is caused by their enhancement of intrinsic slow inactivation gating. Modulation of slow inactivation by neurotransmitters acting through G protein-coupled receptors, PKA, and PKC is a flexible mechanism of cellular plasticity controlling the firing behavior of central neurons.
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Affiliation(s)
- Yuan Chen
- Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA
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50
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Abstract
Voltage-gated sodium channels open (activate) when the membrane is depolarized and close on repolarization (deactivate) but also on continuing depolarization by a process termed inactivation, which leaves the channel refractory, i.e., unable to open again for a period of time. In the “classical” fast inactivation, this time is of the millisecond range, but it can last much longer (up to seconds) in a different slow type of inactivation. These two types of inactivation have different mechanisms located in different parts of the channel molecule: the fast inactivation at the cytoplasmic pore opening which can be closed by a hinged lid, the slow inactivation in other parts involving conformational changes of the pore. Fast inactivation is highly vulnerable and affected by many chemical agents, toxins, and proteolytic enzymes but also by the presence of β-subunits of the channel molecule. Systematic studies of these modulating factors and of the effects of point mutations (experimental and in hereditary diseases) in the channel molecule have yielded a fairly consistent picture of the molecular background of fast inactivation, which for the slow inactivation is still lacking.
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Affiliation(s)
- Werner Ulbricht
- Psychologisches Institut, University of Kiel, Hermann-Rodewald-Strasse 5, D-24118 Kiel, Germany.
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