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Subtype-specific modulation of human K V 7 channels by the anticonvulsant cannabidiol through a lipid-exposed pore-domain site. Br J Pharmacol 2023; 180:2956-2972. [PMID: 37377025 DOI: 10.1111/bph.16183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 05/16/2023] [Accepted: 06/13/2023] [Indexed: 06/29/2023] Open
Abstract
BACKGROUND AND PURPOSE Cannabidiol (CBD) is used clinically as an anticonvulsant. Its precise mechanism of action has remained unclear. CBD was recently demonstrated to enhance the activity of the neuronal KV 7.2/7.3 channel, which may be one important contributor to CBD anticonvulsant effect. Curiously, CBD inhibits the closely related cardiac KV 7.1/KCNE1 channel. Whether and how CBD affects other KV 7 subtypes remains uninvestigated and the CBD interaction sites mediating these diverse effects remain unknown. EXPERIMENTAL APPROACH Here, we used electrophysiology, molecular dynamics simulations, molecular docking and site-directed mutagenesis to address these questions. KEY RESULTS We found that CBD modulates the activity of all human KV 7 subtypes and that the effects are subtype dependent. CBD enhanced the activity of KV 7.2-7.5 subtypes, seen as a V50 shift towards more negative voltages or increased maximum conductance. In contrast, CBD inhibited the KV 7.1 and KV 7.1/KCNE1 channels, seen as a V50 shift towards more positive voltages and reduced conductance. In KV 7.2 and KV 7.4, we propose a CBD interaction site at the subunit interface in the pore domain that overlaps with the interaction site of other compounds, notably the anticonvulsant retigabine. However, CBD relies on other residues for its effects than the conserved tryptophan that is critical for retigabine effects. We propose a similar, though not identical CBD site in KV 7.1, with a non-conserved phenylalanine being important. CONCLUSIONS AND IMPLICATIONS We identify novel targets of CBD, contributing to a better understanding of CBD clinical effects and provide mechanistic insights into how CBD modulates different KV 7 subtypes.
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Mechanistic understanding of KCNQ1 activating polyunsaturated fatty acid analogs. J Gen Physiol 2023; 155:e202313339. [PMID: 37526928 PMCID: PMC10394376 DOI: 10.1085/jgp.202313339] [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: 01/12/2023] [Revised: 05/02/2023] [Accepted: 07/18/2023] [Indexed: 08/02/2023] Open
Abstract
The KCNQ1 channel is important for the repolarization phase of the cardiac action potential. Loss of function mutations in KCNQ1 can cause long QT syndrome (LQTS), which can lead to cardiac arrythmia and even sudden cardiac death. We have previously shown that polyunsaturated fatty acids (PUFAs) and PUFA analogs can activate the cardiac KCNQ1 channel, making them potential therapeutics for the treatment of LQTS. PUFAs bind to KCNQ1 at two different binding sites: one at the voltage sensor (Site I) and one at the pore (Site II). PUFA interaction at Site I shifts the voltage dependence of the channel to the left, while interaction at Site II increases maximal conductance. The PUFA analogs, linoleic-glycine and linoleic-tyrosine, are more effective than linoleic acid at Site I, but less effective at Site II. Using both simulations and experiments, we find that the larger head groups of linoleic-glycine and linoleic-tyrosine interact with more residues than the smaller linoleic acid at Site I. We propose that this will stabilize the negatively charged PUFA head group in a position to better interact electrostatically with the positively charges in the voltage sensor. In contrast, the larger head groups of linoleic-glycine and linoleic-tyrosine compared with linoleic acid prevent a close fit of these PUFA analogs in Site II, which is more confined. In addition, we identify several KCNQ1 residues as critical PUFA-analog binding residues, thereby providing molecular models of specific interactions between PUFA analogs and KCNQ1. These interactions will aid in future drug development based on PUFA-KCNQ1 channel interactions.
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Pharmacological Screening of Kv7.1 and Kv7.1/KCNE1 Activators as Potential Antiarrhythmic Drugs in the Zebrafish Heart. Int J Mol Sci 2023; 24:12092. [PMID: 37569465 PMCID: PMC10418701 DOI: 10.3390/ijms241512092] [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: 07/06/2023] [Revised: 07/24/2023] [Accepted: 07/25/2023] [Indexed: 08/13/2023] Open
Abstract
Long QT syndrome (LQTS) can lead to ventricular arrhythmia and sudden cardiac death. The most common congenital cause of LQTS is mutations in the channel subunits generating the cardiac potassium current IKs. Zebrafish (Danio rerio) have been proposed as a powerful system to model human cardiac diseases due to the similar electrical properties of the zebrafish heart and the human heart. We used high-resolution all-optical electrophysiology on ex vivo zebrafish hearts to assess the effects of IKs analogues on the cardiac action potential. We found that chromanol 293B (an IKs inhibitor) prolonged the action potential duration (APD) in the presence of E4031 (an IKr inhibitor applied to drug-induced LQT2), and to a lesser extent, in the absence of E4031. Moreover, we showed that PUFA analogues slightly shortened the APD of the zebrafish heart. However, PUFA analogues failed to reverse the APD prolongation in drug-induced LQT2. However, a more potent IKs activator, ML-277, partially reversed the APD prolongation in drug-induced LQT2 zebrafish hearts. Our results suggest that IKs plays a limited role in ventricular repolarizations in the zebrafish heart under resting conditions, although it plays a more important role when the IKr is compromised, as if the IKs in zebrafish serves as a repolarization reserve as in human hearts. This study shows that potent IKs activators can restore the action potential duration in drug-induced LQT2 in the zebrafish heart.
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Mechanistic insights into robust cardiac I Ks potassium channel activation by aromatic polyunsaturated fatty acid analogues. eLife 2023; 12:e85773. [PMID: 37350568 DOI: 10.7554/elife.85773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Accepted: 06/22/2023] [Indexed: 06/24/2023] Open
Abstract
Voltage-gated potassium (KV) channels are important regulators of cellular excitability and control action potential repolarization in the heart and brain. KV channel mutations lead to disordered cellular excitability. Loss-of-function mutations, for example, result in membrane hyperexcitability, a characteristic of epilepsy and cardiac arrhythmias. Interventions intended to restore KV channel function have strong therapeutic potential in such disorders. Polyunsaturated fatty acids (PUFAs) and PUFA analogues comprise a class of KV channel activators with potential applications in the treatment of arrhythmogenic disorders such as Long QT Syndrome (LQTS). LQTS is caused by a loss-of-function of the cardiac IKs-- channel - a tetrameric potassium channel complex formed by KV7.1 and associated KCNE1 protein subunits. We have discovered a set of aromatic PUFA analogues that produce robust activation of the cardiac IKs channel and a unique feature of these PUFA analogues is an aromatic, tyrosine head group. We determine the mechanisms through which tyrosine PUFA analogues exert strong activating effects on the IKs channel by generating modified aromatic head groups designed to probe cation-pi interactions, hydrogen bonding, and ionic interactions. We found that tyrosine PUFA analogues do not activate the IKs channel through cation-pi interactions, but instead do so through a combination of hydrogen bonding and ionic interactions.
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Long-QT mutations in KCNE1 modulate the 17β-estradiol response of Kv7.1/KCNE1. SCIENCE ADVANCES 2023; 9:eade7109. [PMID: 36921038 PMCID: PMC10017040 DOI: 10.1126/sciadv.ade7109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Accepted: 02/13/2023] [Indexed: 06/18/2023]
Abstract
Estradiol (17[Formula: see text]-E2) is implicated in higher arrhythmia risk of women with congenital or acquired long-QT syndrome (LQTS) compared to men. However, the underlying mechanisms remain poorly understood, and little is known about the impact of LQTS-associated mutations. We show that 17[Formula: see text]-E2 inhibits the human cardiac Kv7.1/KCNE1 channel expressed in Xenopus oocytes. We find that the 17[Formula: see text]-E2 effect depends on the Kv7.1 to KCNE1 stoichiometry, and we reveal a critical function of the KCNE1 carboxyl terminus for the effect. LQTS-associated mutations in the KCNE1 carboxyl terminus show a range of responses to 17[Formula: see text]-E2, from a wild-type like response to impaired or abolished response. Together, this study increases our understanding of the mechanistic basis for 17[Formula: see text]-E2 inhibition of Kv7.1/KCNE1 and demonstrates mutation-dependent responses to 17[Formula: see text]-E2. These findings suggest that the 17[Formula: see text]-E2 effect on Kv7.1/KCNE1 might contribute to the higher arrhythmia risk of women, particularly in carriers with specific LQTS-associated mutations.
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Endocannabinoids enhance hK V7.1/KCNE1 channel function and shorten the cardiac action potential and QT interval. EBioMedicine 2023; 89:104459. [PMID: 36796231 PMCID: PMC9958262 DOI: 10.1016/j.ebiom.2023.104459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 01/11/2023] [Accepted: 01/18/2023] [Indexed: 02/15/2023] Open
Abstract
BACKGROUND Genotype-positive patients who suffer from the cardiac channelopathy Long QT Syndrome (LQTS) may display a spectrum of clinical phenotypes, with often unknown causes. Therefore, there is a need to identify factors influencing disease severity to move towards an individualized clinical management of LQTS. One possible factor influencing the disease phenotype is the endocannabinoid system, which has emerged as a modulator of cardiovascular function. In this study, we aim to elucidate whether endocannabinoids target the cardiac voltage-gated potassium channel KV7.1/KCNE1, which is the most frequently mutated ion channel in LQTS. METHODS We used two-electrode voltage clamp, molecular dynamics simulations and the E4031 drug-induced LQT2 model of ex-vivo guinea pig hearts. FINDINGS We found a set of endocannabinoids that facilitate channel activation, seen as a shifted voltage-dependence of channel opening and increased overall current amplitude and conductance. We propose that negatively charged endocannabinoids interact with known lipid binding sites at positively charged amino acids on the channel, providing structural insights into why only specific endocannabinoids modulate KV7.1/KCNE1. Using the endocannabinoid ARA-S as a prototype, we show that the effect is not dependent on the KCNE1 subunit or the phosphorylation state of the channel. In guinea pig hearts, ARA-S was found to reverse the E4031-prolonged action potential duration and QT interval. INTERPRETATION We consider the endocannabinoids as an interesting class of hKV7.1/KCNE1 channel modulators with putative protective effects in LQTS contexts. FUNDING ERC (No. 850622), Canadian Institutes of Health Research, Canada Research Chairs and Compute Canada, Swedish National Infrastructure for Computing.
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Development of IKs activating compounds for treatment of long QT syndrome. Biophys J 2023; 122:13a. [PMID: 36782633 DOI: 10.1016/j.bpj.2022.11.298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
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8
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The endocannabinoid ARA-S displays variably activating effects on K v7.1/KCNE1 carrying long QT syndrome mutations. Biophys J 2023; 122:253a. [PMID: 36783245 DOI: 10.1016/j.bpj.2022.11.1464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
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9
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Mechanistic insights into robust cardiac I Ks potassium channel activation by aromatic polyunsaturated fatty acid analogues. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.12.523777. [PMID: 36711783 PMCID: PMC9882137 DOI: 10.1101/2023.01.12.523777] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Voltage-gated potassium (K V ) channels are important regulators of cellular excitability and control action potential repolarization in the heart and brain. K V channel mutations lead to disordered cellular excitability. Loss-of-function mutations, for example, result in membrane hyperexcitability, a characteristic of epilepsy and cardiac arrhythmias. Interventions intended to restore K V channel function have strong therapeutic potential in such disorders. Polyunsaturated fatty acids (PUFAs) and PUFA analogues comprise a class of K V channel activators with potential applications in the treatment of arrhythmogenic disorders such as Long QT Syndrome (LQTS). LQTS is caused by a loss-of-function of the cardiac I Ks channel - a tetrameric potassium channel complex formed by K V 7.1 and associated KCNE1 protein subunits. We have discovered a set of aromatic PUFA analogues that produce robust activation of the cardiac I Ks channel and a unique feature of these PUFA analogues is an aromatic, tyrosine head group. We determine the mechanisms through which tyrosine PUFA analogues exert strong activating effects on the I Ks channel by generating modified aromatic head groups designed to probe cation-pi interactions, hydrogen bonding, and ionic interactions. We found that tyrosine PUFA analogues do not activate the I Ks channel through cation-pi interactions, but instead do so through a combination of hydrogen bonding and ionic interactions.
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ASIC3, a proton-gated ion channel with preference for polyunsaturated lipids with specific headgroup and tail properties. J Gen Physiol 2022; 154:e202213171. [PMID: 35583814 PMCID: PMC9121178 DOI: 10.1085/jgp.202213171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Commentary highlighting valuable mechanistic insights provided by Klipp and Bankston on ASIC3 regulation by lipids.
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Subtype-specific responses of hKv7.4 and hKv7.5 channels to polyunsaturated fatty acids reveal an unconventional modulatory site and mechanism. eLife 2022; 11:77672. [PMID: 35642964 PMCID: PMC9159753 DOI: 10.7554/elife.77672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Accepted: 05/11/2022] [Indexed: 11/13/2022] Open
Abstract
The KV7.4 and KV7.5 subtypes of voltage-gated potassium channels play a role in important physiological processes such as sound amplification in the cochlea and adjusting vascular smooth muscle tone. Therefore, the mechanisms that regulate KV7.4 and KV7.5 channel function are of interest. Here, we study the effect of polyunsaturated fatty acids (PUFAs) on human KV7.4 and KV7.5 channels expressed in Xenopus oocytes. We report that PUFAs facilitate activation of hKV7.5 by shifting the V50 of the conductance versus voltage (G(V)) curve toward more negative voltages. This response depends on the head group charge, as an uncharged PUFA analogue has no effect and a positively charged PUFA analogue induces positive V50 shifts. In contrast, PUFAs inhibit activation of hKV7.4 by shifting V50 toward more positive voltages. No effect on V50 of hKV7.4 is observed by an uncharged or a positively charged PUFA analogue. Thus, the hKV7.5 channel's response to PUFAs is analogous to the one previously observed in hKV7.1-7.3 channels, whereas the hKV7.4 channel response is opposite, revealing subtype-specific responses to PUFAs. We identify a unique inner PUFA interaction site in the voltage-sensing domain of hKV7.4 underlying the PUFA response, revealing an unconventional mechanism of modulation of hKV7.4 by PUFAs.
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12
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Human kV7 channel subtypes are differentially modulated by cannabidiol. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.1544] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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13
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Endocannabinoid-like compounds as modulators of the cardiac kv7.1/KCNE1 channel. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.1546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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14
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Cannabidiol differentially modulates Kv7 channelopathy-related phenotypes. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Faradaic Pixels for Precise Hydrogen Peroxide Delivery to Control M-Type Voltage-Gated Potassium Channels. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2103132. [PMID: 34825522 PMCID: PMC8787424 DOI: 10.1002/advs.202103132] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 10/28/2021] [Indexed: 06/13/2023]
Abstract
H2 O2 plays a significant role in a range of physiological processes where it performs vital tasks in redox signaling. The sensitivity of many biological pathways to H2 O2 opens up a unique direction in the development of bioelectronics devices to control levels of reactive-oxygen species (ROS). Here a microfabricated ROS modulation device that relies on controlled faradaic reactions is presented. A concentric pixel arrangement of a peroxide-evolving cathode surrounded by an anode ring which decomposes the peroxide, resulting in localized peroxide delivery is reported. The conducting polymer (poly(3,4-ethylenedioxythiophene) (PEDOT), is exploited as the cathode. PEDOT selectively catalyzes the oxygen reduction reaction resulting in the production of hydrogen peroxide (H2 O2 ). Using electrochemical and optical assays, combined with modeling, the performance of the devices is benchmarked. The concentric pixels generate tunable gradients of peroxide and oxygen concentrations. The faradaic devices are prototyped by modulating human H2 O2 -sensitive Kv7.2/7.3 (M-type) channels expressed in a single-cell model (Xenopus laevis oocytes). The Kv7 ion channel family is responsible for regulating neuronal excitability in the heart, brain, and smooth muscles, making it an ideal platform for faradaic ROS stimulation. The results demonstrate the potential of PEDOT to act as an H2 O2 delivery system, paving the way to ROS-based organic bioelectronics.
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Docosahexaenoic acid normalizes QT interval in long QT type 2 transgenic rabbit models in a genotype-specific fashion. Europace 2021; 24:511-522. [PMID: 34601592 DOI: 10.1093/europace/euab228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 08/11/2021] [Indexed: 11/13/2022] Open
Abstract
AIM Long QT syndrome (LQTS) is a cardiac channelopathy predisposing to ventricular arrhythmias and sudden cardiac death. Since current therapies often fail to prevent arrhythmic events in certain LQTS subtypes, new therapeutic strategies are needed. Docosahexaenoic acid (DHA) is a polyunsaturated fatty acid, which enhances the repolarizing IKs current. METHODS AND RESULTS We investigated the effects of DHA in wild type (WT) and transgenic long QT Type 1 (LQT1; loss of IKs), LQT2 (loss of IKr), LQT5 (reduction of IKs), and LQT2-5 (loss of IKr and reduction of IKs) rabbits. In vivo ECGs were recorded at baseline and after 10 µM/kg DHA to assess changes in heart-rate corrected QT (QTc) and short-term variability of QT (STVQT). Ex vivo monophasic action potentials were recorded in Langendorff-perfused rabbit hearts, and action potential duration (APD75) and triangulation were assessed. Docosahexaenoic acid significantly shortened QTc in vivo only in WT and LQT2 rabbits, in which both α- and β-subunits of IKs-conducting channels are functionally intact. In LQT2, this led to a normalization of QTc and of its short-term variability. Docosahexaenoic acid had no effect on QTc in LQT1, LQT5, and LQT2-5. Similarly, ex vivo, DHA shortened APD75 in WT and normalized it in LQT2, and additionally decreased AP triangulation in LQT2. CONCLUSIONS Docosahexaenoic acid exerts a genotype-specific beneficial shortening/normalizing effect on QTc and APD75 and reduces pro-arrhythmia markers STVQT and AP triangulation through activation of IKs in LQT2 rabbits but has no effects if either α- or β-subunits to IKs are functionally impaired. Docosahexaenoic acid could represent a new genotype-specific therapy in LQT2.
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Combining endocannabinoids with retigabine for enhanced M-channel effect and improved KV7 subtype selectivity. J Gen Physiol 2021; 152:151732. [PMID: 32365171 PMCID: PMC7398146 DOI: 10.1085/jgp.202012576] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Accepted: 03/25/2020] [Indexed: 12/22/2022] Open
Abstract
Retigabine is unique among anticonvulsant drugs by targeting the neuronal M-channel, which is composed of KV7.2/KV7.3 and contributes to the negative neuronal resting membrane potential. Unfortunately, retigabine causes adverse effects, which limits its clinical use. Adverse effects may be reduced by developing M-channel activators with improved KV7 subtype selectivity. The aim of this study was to evaluate the prospect of endocannabinoids as M-channel activators, either in isolation or combined with retigabine. Human KV7 channels were expressed in Xenopus laevis oocytes. The effect of extracellular application of compounds with different properties was studied using two-electrode voltage clamp electrophysiology. Site-directed mutagenesis was used to construct channels with mutated residues to aid in the mechanistic understanding of these effects. We find that arachidonoyl-L-serine (ARA-S), a weak endocannabinoid, potently activates the human M-channel expressed in Xenopus oocytes. Importantly, we show that ARA-S activates the M-channel via a different mechanism and displays a different KV7 subtype selectivity compared with retigabine. We demonstrate that coapplication of ARA-S and retigabine at low concentrations retains the effect on the M-channel while limiting effects on other KV7 subtypes. Our findings suggest that improved KV7 subtype selectivity of M-channel activators can be achieved through strategically combining compounds with different subtype selectivity.
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Polyunsaturated fatty acids produce a range of activators for heterogeneous IKs channel dysfunction. J Gen Physiol 2021; 152:133474. [PMID: 31865382 PMCID: PMC7062506 DOI: 10.1085/jgp.201912396] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 09/05/2019] [Accepted: 11/27/2019] [Indexed: 01/28/2023] Open
Abstract
Repolarization and termination of the ventricular cardiac action potential is highly dependent on the activation of the slow delayed-rectifier potassium IKs channel. Disruption of the IKs current leads to the most common form of congenital long QT syndrome (LQTS), a disease that predisposes patients to ventricular arrhythmias and sudden cardiac death. We previously demonstrated that polyunsaturated fatty acid (PUFA) analogues increase outward K+ current in wild type and LQTS-causing mutant IKs channels. Our group has also demonstrated the necessity of a negatively charged PUFA head group for potent activation of the IKs channel through electrostatic interactions with the voltage-sensing and pore domains. Here, we test whether the efficacy of the PUFAs can be tuned by the presence of different functional groups in the PUFA head, thereby altering the electrostatic interactions of the PUFA head group with the voltage sensor or the pore. We show that PUFA analogues with taurine and cysteic head groups produced the most potent activation of IKs channels, largely by shifting the voltage dependence of activation. In comparison, the effect on voltage dependence of PUFA analogues with glycine and aspartate head groups was half that of the taurine and cysteic head groups, whereas the effect on maximal conductance was similar. Increasing the number of potentially negatively charged moieties did not enhance the effects of the PUFA on the IKs channel. Our results show that one can tune the efficacy of PUFAs on IKs channels by altering the pKa of the PUFA head group. Different PUFAs with different efficacy on IKs channels could be developed into more personalized treatments for LQTS patients with a varying degree of IKs channel dysfunction.
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Identification of PUFA interaction sites on the cardiac potassium channel KCNQ1. J Gen Physiol 2021; 153:212043. [PMID: 33939797 PMCID: PMC8097404 DOI: 10.1085/jgp.202012850] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/19/2021] [Accepted: 04/17/2021] [Indexed: 12/16/2022] Open
Abstract
Polyunsaturated fatty acids (PUFAs), but not saturated fatty acids, modulate ion channels such as the cardiac KCNQ1 channel, although the mechanism is not completely understood. Using both simulations and experiments, we find that PUFAs interact directly with the KCNQ1 channel via two different binding sites: one at the voltage sensor and one at the pore. These two amphiphilic binding pockets stabilize the negatively charged PUFA head group by electrostatic interactions with R218, R221, and K316, while the hydrophobic PUFA tail is selectively stabilized by cassettes of hydrophobic residues. The rigid saturated tail of stearic acid prevents close contacts with KCNQ1. By contrast, the mobile tail of PUFA linoleic acid can be accommodated in the crevice of the hydrophobic cassette, a defining feature of PUFA selectivity in KCNQ1. In addition, we identify Y268 as a critical PUFA anchor point underlying fatty acid selectivity. Combined, this study provides molecular models of direct interactions between PUFAs and KCNQ1 and identifies selectivity mechanisms. Long term, this understanding may open new avenues for drug development based on PUFA mechanisms.
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Rational Design of Fatty Acid Analogues Targeting the Cardiac KV7.1 Channel. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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21
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Polyunsaturated fatty acid-derived I Ks channel activators shorten the QT interval ex-vivo and in-vivo. Acta Physiol (Oxf) 2020; 229:e13471. [PMID: 32223014 PMCID: PMC8633721 DOI: 10.1111/apha.13471] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 03/17/2020] [Accepted: 03/18/2020] [Indexed: 12/16/2022]
Abstract
AIM We aimed to assess the ability of natural and modified polyunsaturated fatty acids (PUFAs) to shorten QT interval in ex-vivo and in-vivo guinea pig hearts. METHODS The effect of one natural (docosahexaenoic acid [DHA]) and three modified (linoleoyl glycine [Lin-GLY], docosahexaenoyl glycine [DHA-GLY], N-arachidonoyl taurine [N-AT]) PUFAs on ventricular action potential duration (APD) and QT interval was studied in a E4031 drug-induced long QT2 model of ex-vivo guinea pig hearts. The effect of DHA-GLY on QT interval was also studied in in-vivo guinea pig hearts upon intravenous administration. The effect of modified PUFAs on IKs was studied using Xenopus laevis oocytes expressing human KCNQ1 and KCNE1. RESULTS All tested PUFAs shortened ADP and QT interval in ex-vivo guinea pig hearts, however, with different ability in restoring baseline APD/QT interval with specific modified PUFAs being most efficacious. Despite comparable ability in activating the human KCNQ1/KCNE1 channel, Lin-GLY was not as effective in shortening APD/QT interval as DHA-GLY in ex-vivo hearts. By constructing a guinea pig-like KCNE1, we found Lin-GLY to induce less activating effect compared with DHA-GLY on human KCNQ1 co-expressed with guinea pig-like KCNE1. Docosahexaenoyl glycine was studied in more detail and was found to shorten QT interval in in-vivo guinea pig hearts. CONCLUSION Our results show that specific PUFAs shorten QT interval in guinea pig hearts. The tendency of modified PUFAs with pronounced IKs channel activating effect to better restore QT interval suggests that modifying PUFAs to target the IKs channel is a means to improve the QT-shortening effect.
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Polyunsaturated Fatty Acids as Modulators of K V7 Channels. Front Physiol 2020; 11:641. [PMID: 32595524 PMCID: PMC7300222 DOI: 10.3389/fphys.2020.00641] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 05/20/2020] [Indexed: 11/25/2022] Open
Abstract
Voltage-gated potassium channels of the KV7 family are expressed in many tissues. The physiological importance of KV7 channels is evident from specific forms of disorders linked to dysfunctional KV7 channels, including variants of epilepsy, cardiac arrhythmia and hearing impairment. Thus, understanding how KV7 channels are regulated in the body is of great interest. This Mini Review focuses on the effects of polyunsaturated fatty acids (PUFAs) on KV7 channel activity and possible underlying mechanisms of action. By summarizing reported effects of PUFAs on KV7 channels and native KV7-mediated currents, we conclude that the generally observed effect is a PUFA-induced increase in current amplitude. The increase in current is commonly associated with a shift in the voltage-dependence of channel opening and in some cases with increased maximum conductance. Auxiliary KCNE subunits, which associate with KV7 channels in certain tissues, may influence PUFA effects, though findings are conflicting. Both direct and indirect activating PUFA effects have been described, direct effects having been most extensively studied on KV7.1. The negative charge of the PUFA head-group has been identified as critical for electrostatic interaction with conserved positively charged amino acids in transmembrane segments 4 and 6. Additionally, the localization of double bonds in the PUFA tail tunes the apparent affinity of PUFAs to KV7.1. Indirect effects include those mediated by PUFA metabolites. Indirect inhibitory effects involve KV7 channel degradation and re-distribution from lipid rafts. Understanding how PUFAs regulate KV7 channels may provide insight into physiological regulation of KV7 channels and bring forth new therapeutic strategies.
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Correction: Polyunsaturated fatty acid analogues differentially affect cardiac Na V, Ca V, and K V channels through unique mechanisms. eLife 2020; 9:60141. [PMID: 32553105 PMCID: PMC7302875 DOI: 10.7554/elife.60141] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Polyunsaturated fatty acid analogues differentially affect cardiac Na V, Ca V, and K V channels through unique mechanisms. eLife 2020; 9:51453. [PMID: 32207683 PMCID: PMC7159882 DOI: 10.7554/elife.51453] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Accepted: 03/24/2020] [Indexed: 12/15/2022] Open
Abstract
The cardiac ventricular action potential depends on several voltage-gated ion channels, including NaV, CaV, and KV channels. Mutations in these channels can cause Long QT Syndrome (LQTS) which increases the risk for ventricular fibrillation and sudden cardiac death. Polyunsaturated fatty acids (PUFAs) have emerged as potential therapeutics for LQTS because they are modulators of voltage-gated ion channels. Here we demonstrate that PUFA analogues vary in their selectivity for human voltage-gated ion channels involved in the ventricular action potential. The effects of specific PUFA analogues range from selective for a specific ion channel to broadly modulating cardiac ion channels from all three families (NaV, CaV, and KV). In addition, a PUFA analogue selective for the cardiac IKs channel (Kv7.1/KCNE1) is effective in shortening the cardiac action potential in human-induced pluripotent stem cell-derived cardiomyocytes. Our data suggest that PUFA analogues could potentially be developed as therapeutics for LQTS and cardiac arrhythmia.
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Mechanisms Underlying the Dual Effect of Polyunsaturated Fatty Acid Analogs on Kv7.1. Cell Rep 2019; 24:2908-2918. [PMID: 30208316 DOI: 10.1016/j.celrep.2018.08.031] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Revised: 07/17/2018] [Accepted: 08/13/2018] [Indexed: 01/29/2023] Open
Abstract
Polyunsaturated fatty acid (PUFA) analogs represent a new class of potential anti-arrhythmic KV7.1 and KV7.1+KCNE1 channel activators. In this study, we describe dual independent activating effects of negatively charged PUFA analogs on KV7.1 and KV7.1+KCNE1 that are dependent on discrete channel motifs. PUFA analogs are critically dependent on K326 in S6 of KV7.1 to increase the maximum conductance and critically dependent on specific S4 arginines in KV7.1 to shift the voltage dependence of channel opening toward negative voltages. Our findings provide insights into how KV7.1+KCNE1 activators may interact electrostatically both with the pore domain and the voltage-sensing domain to augment channel activity. We believe that the molecular understanding of how PUFA analogs induce dual independent activating effects is an important step toward the development of effective anti-arrhythmic drugs that target KV7.1 channels.
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Effect of Lipophilic Molecules on Epilepsy-Causing Mutations of Neuronal KCNQ Channels. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.2907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes as Early-Screening Platform of Anti-Arrhythmic Effects by Pufas. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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ω-6 and ω-9 polyunsaturated fatty acids with double bonds near the carboxyl head have the highest affinity and largest effects on the cardiac I K s potassium channel. Acta Physiol (Oxf) 2019; 225:e13186. [PMID: 30184322 PMCID: PMC6335172 DOI: 10.1111/apha.13186] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 08/30/2018] [Accepted: 09/02/2018] [Indexed: 02/06/2023]
Abstract
Aim The IKs channel is important for termination of the cardiac action potential. Hundreds of loss‐of‐function mutations in the IKs channel reduce the K+ current and, thereby, delay the repolarization of the action potential, causing Long QT Syndrome. Long QT predisposes individuals to Torsades de Pointes which can lead to ventricular fibrillation and sudden death. Polyunsaturated fatty acids (PUFAs) are potential therapeutics for Long QT Syndrome, as they affect IKs channels. However, it is unclear which properties of PUFAs are essential for their effects on IKs channels. Methods To understand how PUFAs influence IKs channel activity, we measured effects on IKs current by two‐electrode voltage clamp while changing different properties of the hydrocarbon tail. Results There was no, or weak, correlation between the tail length or number of double bonds in the tail and the effects on or apparent binding affinity for IKs channels. However, we found a strong correlation between the positions of the double bonds relative to the head group and effects on IKs channels. Conclusion Polyunsaturated fatty acids with double bonds closer to the head group had higher apparent affinity for IKs channels and increased IKs current more; shifting the bonds further away from the head group reduced apparent binding affinity for and effects on the IKs current. Interestingly, we found that ω‐6 and ω‐9 PUFAs, with the first double bond closer to the head group, left‐shifted the voltage dependence of activation the most. These results allow for informed design of new therapeutics targeting IKs channels in Long QT Syndrome.
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KCNE1 tunes the sensitivity of K V7.1 to polyunsaturated fatty acids by moving turret residues close to the binding site. eLife 2018; 7:37257. [PMID: 30014849 PMCID: PMC6080945 DOI: 10.7554/elife.37257] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2018] [Accepted: 07/15/2018] [Indexed: 12/23/2022] Open
Abstract
The voltage-gated potassium channel KV7.1 and the auxiliary subunit KCNE1 together form the cardiac IKs channel, which is a proposed target for future anti-arrhythmic drugs. We previously showed that polyunsaturated fatty acids (PUFAs) activate KV7.1 via an electrostatic mechanism. The activating effect was abolished when KV7.1 was co-expressed with KCNE1, as KCNE1 renders PUFAs ineffective by promoting PUFA protonation. PUFA protonation reduces the potential of PUFAs as anti-arrhythmic compounds. It is unknown how KCNE1 promotes PUFA protonation. Here, we found that neutralization of negatively charged residues in the S5-P-helix loop of KV7.1 restored PUFA effects on KV7.1 co-expressed with KCNE1 in Xenopus oocytes. We propose that KCNE1 moves the S5-P-helix loop of KV7.1 towards the PUFA-binding site, which indirectly causes PUFA protonation, thereby reducing the effect of PUFAs on KV7.1. This mechanistic understanding of how KCNE1 alters KV7.1 pharmacology is essential for development of drugs targeting the IKs channel.
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Biaryl sulfonamide motifs up- or down-regulate ion channel activity by activating voltage sensors. J Gen Physiol 2018; 150:1215-1230. [PMID: 30002162 PMCID: PMC6080886 DOI: 10.1085/jgp.201711942] [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: 11/09/2017] [Revised: 04/20/2018] [Accepted: 06/11/2018] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated ion channels are key molecules for the generation of cellular electrical excitability. Many pharmaceutical drugs target these channels by blocking their ion-conducting pore, but in many cases, channel-opening compounds would be more beneficial. Here, to search for new channel-opening compounds, we screen 18,000 compounds with high-throughput patch-clamp technology and find several potassium-channel openers that share a distinct biaryl-sulfonamide motif. Our data suggest that the negatively charged variants of these compounds bind to the top of the voltage-sensor domain, between transmembrane segments 3 and 4, to open the channel. Although we show here that biaryl-sulfonamide compounds open a potassium channel, they have also been reported to block sodium and calcium channels. However, because they inactivate voltage-gated sodium channels by promoting activation of one voltage sensor, we suggest that, despite different effects on the channel gates, the biaryl-sulfonamide motif is a general ion-channel activator motif. Because these compounds block action potential-generating sodium and calcium channels and open an action potential-dampening potassium channel, they should have a high propensity to reduce excitability. This opens up the possibility to build new excitability-reducing pharmaceutical drugs from the biaryl-sulfonamide scaffold.
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Molecular Mechanism of Polyunsaturated Fatty Acid Analogues as KV7.1-Channel Modulators. Biophys J 2018. [DOI: 10.1016/j.bpj.2017.11.695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Abstract
Barro-Soria et al. highlight work that reveals how β1 and β3 subunits modulate NaV1.5 channel function.
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Actions and Mechanisms of Polyunsaturated Fatty Acids on Voltage-Gated Ion Channels. Front Physiol 2017; 8:43. [PMID: 28220076 PMCID: PMC5292575 DOI: 10.3389/fphys.2017.00043] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 01/16/2017] [Indexed: 01/29/2023] Open
Abstract
Polyunsaturated fatty acids (PUFAs) act on most ion channels, thereby having significant physiological and pharmacological effects. In this review we summarize data from numerous PUFAs on voltage-gated ion channels containing one or several voltage-sensor domains, such as voltage-gated sodium (NaV), potassium (KV), calcium (CaV), and proton (HV) channels, as well as calcium-activated potassium (KCa), and transient receptor potential (TRP) channels. Some effects of fatty acids appear to be channel specific, whereas others seem to be more general. Common features for the fatty acids to act on the ion channels are at least two double bonds in cis geometry and a charged carboxyl group. In total we identify and label five different sites for the PUFAs. PUFA site 1: The intracellular cavity. Binding of PUFA reduces the current, sometimes as a time-dependent block, inducing an apparent inactivation. PUFA site 2: The extracellular entrance to the pore. Binding leads to a block of the channel. PUFA site 3: The intracellular gate. Binding to this site can bend the gate open and increase the current. PUFA site 4: The interface between the extracellular leaflet of the lipid bilayer and the voltage-sensor domain. Binding to this site leads to an opening of the channel via an electrostatic attraction between the negatively charged PUFA and the positively charged voltage sensor. PUFA site 5: The interface between the extracellular leaflet of the lipid bilayer and the pore domain. Binding to this site affects slow inactivation. This mapping of functional PUFA sites can form the basis for physiological and pharmacological modifications of voltage-gated ion channels.
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Molecular Mechanism of the K v 7.1-Channel Activator N-Arachidonoyl Taurine. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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Fatty acid analogue N-arachidonoyl taurine restores function of I Ks channels with diverse long QT mutations. eLife 2016; 5. [PMID: 27690226 PMCID: PMC5081249 DOI: 10.7554/elife.20272] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Accepted: 09/28/2016] [Indexed: 01/08/2023] Open
Abstract
About 300 loss-of-function mutations in the IKs channel have been identified in patients with Long QT syndrome and cardiac arrhythmia. How specific mutations cause arrhythmia is largely unknown and there are no approved IKs channel activators for treatment of these arrhythmias. We find that several Long QT syndrome-associated IKs channel mutations shift channel voltage dependence and accelerate channel closing. Voltage-clamp fluorometry experiments and kinetic modeling suggest that similar mutation-induced alterations in IKs channel currents may be caused by different molecular mechanisms. Finally, we find that the fatty acid analogue N-arachidonoyl taurine restores channel gating of many different mutant channels, even though the mutations are in different domains of the IKs channel and affect the channel by different molecular mechanisms. N-arachidonoyl taurine is therefore an interesting prototype compound that may inspire development of future IKs channel activators to treat Long QT syndrome caused by diverse IKs channel mutations. DOI:http://dx.doi.org/10.7554/eLife.20272.001 Every heartbeat relies on an electric wave that travels through the heart. This wave must reach different parts of the heart in a specific sequence to ensure that the heart muscle cells contract in a coordinated manner. Such coordinated contractions enable the heart to pump enough blood around the body. By allowing specific ions to flow into or out of the heart muscle cell, proteins called ion channels in the cell membrane generate the electric wave, keep it going and stop it. One such protein called the IKs channel controls the flow of potassium ions, and in doing so stops the electric wave in heart muscle cells. About 300 different mutations in the IKs channel have been shown to cause abnormal heart rhythms in individuals with a disorder called long QT syndrome. People with this condition may suddenly black out because their heart develops prolonged electric waves that prevent blood from being pumped properly. To investigate how mutations in the IKs channel produce heart rhythm abnormalities, Liin et al. genetically engineered the egg cells of African clawed frogs to have one of eight mutant forms of the human IKs channel. Studying these channels revealed that the mutations reduce how well the channels work in a wide variety of ways. However, treating the cells with a particular fatty acid helped to normalize how each of the mutant channels worked. Therefore, variants of the fatty acid could potentially form a useful treatment for people with heart rhythm problems caused by mutations in the IKs channel. More studies are needed to confirm whether the fatty acid is as effective at combating the effects of the mutations in whole hearts and animals. As ion channels related to the IKs channel are found in many types of cells, it is also important to investigate whether treatment with the fatty acid could cause any side effects that affect other organs. DOI:http://dx.doi.org/10.7554/eLife.20272.002
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Polyunsaturated fatty acids are potent openers of human M-channels expressed in Xenopus laevis oocytes. Acta Physiol (Oxf) 2016; 218:28-37. [PMID: 26914447 DOI: 10.1111/apha.12663] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2015] [Revised: 11/26/2015] [Accepted: 02/18/2016] [Indexed: 11/26/2022]
Abstract
AIM Polyunsaturated fatty acids have been reported to reduce neuronal excitability, in part by promoting inactivation of voltage-gated sodium and calcium channels. Effects on neuronal potassium channels are less explored and experimental data ambiguous. The aim of this study was to investigate anti-excitable effects of polyunsaturated fatty acids on the neuronal M-channel, important for setting the resting membrane potential in hippocampal and dorsal root ganglion neurones. METHODS Effects of fatty acids and fatty acid analogues on mouse dorsal root ganglion neurones and on the human KV 7.2/3 channel expressed in Xenopus laevis oocytes were studied using electrophysiology. RESULTS Extracellular application of physiologically relevant concentrations of the polyunsaturated fatty acid docosahexaenoic acid hyperpolarized the resting membrane potential (-2.4 mV by 30 μm) and increased the threshold current to evoke action potentials in dorsal root ganglion neurones. The polyunsaturated fatty acids docosahexaenoic acid, α-linolenic acid and eicosapentaenoic acid facilitated opening of the human M-channel, comprised of the heteromeric human KV 7.2/3 channel expressed in Xenopus oocytes, by shifting the conductance-vs.-voltage curve towards more negative voltages (by -7.4 to -11.3 mV by 70 μm). Uncharged docosahexaenoic acid methyl ester and monounsaturated oleic acid did not facilitate opening of the human KV 7.2/3 channel. CONCLUSIONS These findings suggest that circulating polyunsaturated fatty acids, with a minimum requirement of multiple double bonds and a charged carboxyl group, dampen excitability by opening neuronal M-channels. Collectively, our data bring light to the molecular targets of polyunsaturated fatty acids and thus a possible mechanism by which polyunsaturated fatty acids reduce neuronal excitability.
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N-Arachidonoyl Taurine Rescues Diverse Long QT Syndrome-Associated Mutations in the Cardiac I←Ks Channel. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Identification of Residues Important for the PUFA Sensitivity of IKs. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.1504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Abstract
Electrical interfaces between biological cells and man-made electrical devices exist in many forms, but it remains a challenge to bridge the different mechanical and chemical environments of electronic conductors (metals, semiconductors) and biosystems. Here we demonstrate soft electrical interfaces, by integrating the metallic polymer PEDOT-S into lipid membranes. By preparing complexes between alkyl-ammonium salts and PEDOT-S we were able to integrate PEDOT-S into both liposomes and in lipid bilayers on solid surfaces. This is a step towards efficient electronic conduction within lipid membranes. We also demonstrate that the PEDOT-S@alkyl-ammonium:lipid hybrid structures created in this work affect ion channels in the membrane of Xenopus oocytes, which shows the possibility to access and control cell membrane structures with conductive polyelectrolytes.
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The KCNQ1 channel - remarkable flexibility in gating allows for functional versatility. J Physiol 2015; 593:2605-15. [PMID: 25653179 DOI: 10.1113/jphysiol.2014.287607] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 01/30/2015] [Indexed: 12/12/2022] Open
Abstract
The KCNQ1 channel (also called Kv7.1 or KvLQT1) belongs to the superfamily of voltage-gated K(+) (Kv) channels. KCNQ1 shares several general features with other Kv channels but also displays a fascinating flexibility in terms of the mechanism of channel gating, which allows KCNQ1 to play different physiological roles in different tissues. This flexibility allows KCNQ1 channels to function as voltage-independent channels in epithelial tissues, whereas KCNQ1 function as voltage-activated channels with very slow kinetics in cardiac tissues. This flexibility is in part provided by the association of KCNQ1 with different accessory KCNE β-subunits and different modulators, but also seems like an integral part of KCNQ1 itself. The aim of this review is to describe the main mechanisms underlying KCNQ1 flexibility.
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Abstract
Introduction of charged residues into the voltage sensor provides insight into the molecular mechanisms underlying potassium channel sensitivity to polyunsaturated fatty acids. Polyunsaturated fatty acids modulate the voltage dependence of several voltage-gated ion channels, thereby being potent modifiers of cellular excitability. Detailed knowledge of this molecular mechanism can be used in designing a new class of small-molecule compounds against hyperexcitability diseases. Here, we show that arginines on one side of the helical K-channel voltage sensor S4 increased the sensitivity to docosahexaenoic acid (DHA), whereas arginines on the opposing side decreased this sensitivity. Glutamates had opposite effects. In addition, a positively charged DHA-like molecule, arachidonyl amine, had opposite effects to the negatively charged DHA. This suggests that S4 rotates to open the channel and that DHA electrostatically affects this rotation. A channel with arginines in positions 356, 359, and 362 was extremely sensitive to DHA: 70 µM DHA at pH 9.0 increased the current >500 times at negative voltages compared with wild type (WT). The small-molecule compound pimaric acid, a novel Shaker channel opener, opened the WT channel. The 356R/359R/362R channel drastically increased this effect, suggesting it to be instrumental in future drug screening.
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KCNE1 Separates the Main Voltage Sensor Movement and Channel Opening in KCNQ1/KCNE1 Channels. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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Polyunsaturated Fatty acids as Kv7 Channel Modulators. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.1504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Construction of a K Channel Hypersensitive to Polyunsaturated Fatty Acids. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.2565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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