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Angsutararux P, Kang PW, Zhu W, Silva JR. Conformations of voltage-sensing domain III differentially define NaV channel closed- and open-state inactivation. J Gen Physiol 2021; 153:212533. [PMID: 34347027 PMCID: PMC8348240 DOI: 10.1085/jgp.202112891] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 07/14/2021] [Indexed: 11/21/2022] Open
Abstract
Voltage-gated Na+ (NaV) channels underlie the initiation and propagation of action potentials (APs). Rapid inactivation after NaV channel opening, known as open-state inactivation, plays a critical role in limiting the AP duration. However, NaV channel inactivation can also occur before opening, namely closed-state inactivation, to tune the cellular excitability. The voltage-sensing domain (VSD) within repeat IV (VSD-IV) of the pseudotetrameric NaV channel α-subunit is known to be a critical regulator of NaV channel inactivation. Yet, the two processes of open- and closed-state inactivation predominate at different voltage ranges and feature distinct kinetics. How inactivation occurs over these different ranges to give rise to the complexity of NaV channel dynamics is unclear. Past functional studies and recent cryo-electron microscopy structures, however, reveal significant inactivation regulation from other NaV channel components. In this Hypothesis paper, we propose that the VSD of NaV repeat III (VSD-III), together with VSD-IV, orchestrates the inactivation-state occupancy of NaV channels by modulating the affinity of the intracellular binding site of the IFMT motif on the III-IV linker. We review and outline substantial evidence that VSD-III activates in two distinct steps, with the intermediate and fully activated conformation regulating closed- and open-state inactivation state occupancy by altering the formation and affinity of the IFMT crevice. A role of VSD-III in determining inactivation-state occupancy and recovery from inactivation suggests a regulatory mechanism for the state-dependent block by small-molecule anti-arrhythmic and anesthetic therapies.
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Affiliation(s)
- Paweorn Angsutararux
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Po Wei Kang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Wandi Zhu
- Department of Medicine, Brigham and Women's Hospital, Boston, MA
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
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Zhu W, Voelker TL, Varga Z, Schubert AR, Nerbonne JM, Silva JR. Mechanisms of noncovalent β subunit regulation of Na V channel gating. J Gen Physiol 2017; 149:813-831. [PMID: 28720590 PMCID: PMC5560778 DOI: 10.1085/jgp.201711802] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 06/26/2017] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated NaV channels are modulated by two different noncovalent accessory subunits: β1 and β3. Zhu et al. present data showing that β1 and β3 cause distinct effects on channel gating because they interact with NaV channels at different locations. β3 regulates the voltage sensor in domain III, whereas β1 regulates the one in domain IV. Voltage-gated Na+ (NaV) channels comprise a macromolecular complex whose components tailor channel function. Key components are the non-covalently bound β1 and β3 subunits that regulate channel gating, expression, and pharmacology. Here, we probe the molecular basis of this regulation by applying voltage clamp fluorometry to measure how the β subunits affect the conformational dynamics of the cardiac NaV channel (NaV1.5) voltage-sensing domains (VSDs). The pore-forming NaV1.5 α subunit contains four domains (DI–DIV), each with a VSD. Our results show that β1 regulates NaV1.5 by modulating the DIV-VSD, whereas β3 alters channel kinetics mainly through DIII-VSD interaction. Introduction of a quenching tryptophan into the extracellular region of the β3 transmembrane segment inverted the DIII-VSD fluorescence. Additionally, a fluorophore tethered to β3 at the same position produced voltage-dependent fluorescence dynamics strongly resembling those of the DIII-VSD. Together, these results provide compelling evidence that β3 binds proximally to the DIII-VSD. Molecular-level differences in β1 and β3 interaction with the α subunit lead to distinct activation and inactivation recovery kinetics, significantly affecting NaV channel regulation of cell excitability.
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Affiliation(s)
- Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Taylor L Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Zoltan Varga
- MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, University of Debrecen, Debrecen, Hungary
| | - Angela R Schubert
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO.,Department of Internal Medicine, Washington University in St. Louis, St. Louis, MO
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
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Bohnen MS, Peng G, Robey SH, Terrenoire C, Iyer V, Sampson KJ, Kass RS. Molecular Pathophysiology of Congenital Long QT Syndrome. Physiol Rev 2017; 97:89-134. [PMID: 27807201 PMCID: PMC5539372 DOI: 10.1152/physrev.00008.2016] [Citation(s) in RCA: 114] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.
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Affiliation(s)
- M S Bohnen
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - G Peng
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - S H Robey
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - C Terrenoire
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - V Iyer
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - K J Sampson
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
| | - R S Kass
- Department of Pharmacology, Columbia University Medical Center, New York, New York; and The New York Stem Cell Foundation Research Institute, New York, New York
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Ahern CA, Payandeh J, Bosmans F, Chanda B. The hitchhiker's guide to the voltage-gated sodium channel galaxy. ACTA ACUST UNITED AC 2016; 147:1-24. [PMID: 26712848 PMCID: PMC4692491 DOI: 10.1085/jgp.201511492] [Citation(s) in RCA: 234] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Eukaryotic voltage-gated sodium (Nav) channels contribute to the rising phase of action potentials and served as an early muse for biophysicists laying the foundation for our current understanding of electrical signaling. Given their central role in electrical excitability, it is not surprising that (a) inherited mutations in genes encoding for Nav channels and their accessory subunits have been linked to excitability disorders in brain, muscle, and heart; and (b) Nav channels are targeted by various drugs and naturally occurring toxins. Although the overall architecture and behavior of these channels are likely to be similar to the more well-studied voltage-gated potassium channels, eukaryotic Nav channels lack structural and functional symmetry, a notable difference that has implications for gating and selectivity. Activation of voltage-sensing modules of the first three domains in Nav channels is sufficient to open the channel pore, whereas movement of the domain IV voltage sensor is correlated with inactivation. Also, structure–function studies of eukaryotic Nav channels show that a set of amino acids in the selectivity filter, referred to as DEKA locus, is essential for Na+ selectivity. Structures of prokaryotic Nav channels have also shed new light on mechanisms of drug block. These structures exhibit lateral fenestrations that are large enough to allow drugs or lipophilic molecules to gain access into the inner vestibule, suggesting that this might be the passage for drug entry into a closed channel. In this Review, we will synthesize our current understanding of Nav channel gating mechanisms, ion selectivity and permeation, and modulation by therapeutics and toxins in light of the new structures of the prokaryotic Nav channels that, for the time being, serve as structural models of their eukaryotic counterparts.
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Affiliation(s)
- Christopher A Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242
| | - Jian Payandeh
- Department of Structural Biology, Genentech, Inc., South San Francisco, CA 94080
| | - Frank Bosmans
- Department of Physiology and Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD 21205 Department of Physiology and Solomon H. Snyder Department of Neuroscience, Johns Hopkins University, School of Medicine, Baltimore, MD 21205
| | - Baron Chanda
- Department of Neuroscience and Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705 Department of Neuroscience and Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705
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Varga Z, Zhu W, Schubert AR, Pardieck JL, Krumholz A, Hsu EJ, Zaydman MA, Cui J, Silva JR. Direct Measurement of Cardiac Na+ Channel Conformations Reveals Molecular Pathologies of Inherited Mutations. Circ Arrhythm Electrophysiol 2015; 8:1228-39. [PMID: 26283144 DOI: 10.1161/circep.115.003155] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 07/26/2015] [Indexed: 01/11/2023]
Abstract
BACKGROUND Dysregulation of voltage-gated cardiac Na(+) channels (NaV1.5) by inherited mutations, disease-linked remodeling, and drugs causes arrhythmias. The molecular mechanisms whereby the NaV1.5 voltage-sensing domains (VSDs) are perturbed to pathologically or therapeutically modulate Na(+) current (INa) have not been specified. Our aim was to correlate INa kinetics with conformational changes within the 4 (DI-DIV) VSDs to define molecular mechanisms of NaV1.5 modulation. METHOD AND RESULTS Four NaV1.5 constructs were created to track the voltage-dependent kinetics of conformational changes within each VSD, using voltage-clamp fluorometry. Each VSD displayed unique kinetics, consistent with distinct roles in determining INa. In particular, DIII-VSD deactivation kinetics were modulated by depolarizing pulses with durations in the intermediate time domain that modulates late INa. We then used the DII-VSD construct to probe the molecular pathology of 2 Brugada syndrome mutations (A735V and G752R). A735V shifted DII-VSD voltage dependence to depolarized potentials, whereas G752R significantly slowed DII-VSD kinetics. Both mutations slowed INa activation, although DII-VSD activation occurred at higher potentials (A735V) or at later times (G752R) than ionic current activation, indicating that the DII-VSD allosterically regulates the rate of INa activation and myocyte excitability. CONCLUSIONS Our results reveal novel mechanisms whereby the NaV1.5 VSDs regulate channel activation and inactivation. The ability to distinguish distinct molecular mechanisms of proximal Brugada syndrome mutations demonstrates the potential of these methods to reveal how inherited mutations, post-translational modifications, and antiarrhythmic drugs alter NaV1.5 at the molecular level.
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Affiliation(s)
- Zoltan Varga
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Wandi Zhu
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Angela R Schubert
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Jennifer L Pardieck
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Arie Krumholz
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Eric J Hsu
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Mark A Zaydman
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Jianmin Cui
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.)
| | - Jonathan R Silva
- From the Department of Biomedical Engineering, Washington University in St. Louis, MO (Z.V., W.Z., A.R.S., J.L.P., A.K., E.J.H., M.A.Z., J.C., J.R.S.); and MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, Department of Biophysics and Cell Biology, University of Debrecen, Debrecen, Hungary (Z.V.).
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Nakajima T, Kaneko Y, Saito A, Ota M, Iijima T, Kurabayashi M. Enhanced fast-inactivated state stability of cardiac sodium channels by a novel voltage sensor SCN5A mutation, R1632C, as a cause of atypical Brugada syndrome. Heart Rhythm 2015; 12:2296-304. [PMID: 26031372 DOI: 10.1016/j.hrthm.2015.05.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Indexed: 12/19/2022]
Abstract
BACKGROUND Mutations in SCN5A, which encodes the cardiac voltage-gated sodium channels, can be associated with multiple electrophysiological phenotypes. A novel SCN5A R1632C mutation, located in the domain IV-segment 4 voltage sensor, was identified in a young male patient who had a syncopal episode during exercise and presented with atrial tachycardia, sinus node dysfunction, and Brugada syndrome. OBJECTIVE We sought to elucidate the functional consequences of the R1632C mutation. METHODS The wild-type (WT) or R1632C SCN5A mutation was coexpressed with β1 subunit in tsA201 cells, and whole-cell sodium currents (INa) were recorded using patch-clamp methods. RESULTS INa density, measured at -20 mV from a holding potential of -120 mV, for R1632C was significantly lower than that for WT (R1632C: -433 ± 52 pA/pF, n = 14; WT: -672 ± 90 pA/pF, n = 15; P < .05); however, no significant changes were observed in the steady-state activation and fast inactivation rate. The steady-state inactivation curve for R1632C was remarkably shifted to hyperpolarizing potentials compared with that for WT (R1632C: V1/2 = -110.7 ± 0.8 mV, n = 16; WT: V1/2 = -85.9 ± 2.5 mV, n = 17; P < .01). The steady-state fast inactivation curve for R1632C was also shifted to the same degree. Recovery from fast inactivation after a 20-ms depolarizing pulse for R1632C was remarkably delayed compared with that for WT (R1632C: τ = 246.7 ± 14.3 ms, n = 8; WT: τ = 3.7 ± 0.3 ms, n = 8; P < .01). Repetitive depolarizing pulses at various cycle lengths greatly attenuated INa for R1632C than that for WT. CONCLUSION R1632C showed a loss of function of INa by an enhanced fast-inactivated state stability because of a pronounced impairment of recovery from fast inactivation, which may explain the phenotypic manifestation observed in our patient.
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Affiliation(s)
- Tadashi Nakajima
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan.
| | - Yoshiaki Kaneko
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Akihiro Saito
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Masaki Ota
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Takafumi Iijima
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
| | - Masahiko Kurabayashi
- Department of Medicine and Biological Science, Gunma University Graduate School of Medicine, Maebashi, Japan
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Gao R, Du Y, Wang L, Nomura Y, Satar G, Gordon D, Gurevitz M, Goldin AL, Dong K. Sequence variations at I260 and A1731 contribute to persistent currents in Drosophila sodium channels. Neuroscience 2014; 268:297-308. [PMID: 24662849 DOI: 10.1016/j.neuroscience.2014.03.028] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 02/02/2014] [Accepted: 03/09/2014] [Indexed: 12/19/2022]
Abstract
Tetrodotoxin-sensitive persistent sodium currents, INaP, that activate at subthreshold voltages, have been detected in numerous vertebrate and invertebrate neurons. These currents are believed to be critical for regulating neuronal excitability. However, the molecular mechanism underlying INaP is controversial. In this study, we identified an INaP with a broad range of voltage dependence, from -60mV to 20mV, in a Drosophila sodium channel variant expressed in Xenopus oocytes. Mutational analysis revealed that two variant-specific amino acid changes, I260T in the S4-S5 linker of domain I (ILS4-S5) and A1731V in the voltage sensor S4 of domain IV (IVS4), contribute to the INaP. I260T is critical for the portion of INaP at hyperpolarized potentials. The T260-mediated INaP is likely the result of window currents flowing in the voltage range where the activation and inactivation curves overlap. A1731V is responsible for impaired inactivation and contributes to the portion of INaP at depolarized potentials. Furthermore, A1731V causes enhanced activity of two site-3 toxins which induce persistent currents by inhibiting the outward movement of IVS4, suggesting that A1731V inhibits the outward movement of IVS4. These results provided molecular evidence for the involvement of distinct mechanisms in the generation of INaP: T260 contributes to INaP via enhancement of the window current, whereas V1731 impairs fast inactivation probably by inhibiting the outward movement of IVS4.
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Affiliation(s)
- R Gao
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - Y Du
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - L Wang
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - Y Nomura
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - G Satar
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States
| | - D Gordon
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Israel
| | - M Gurevitz
- Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Israel
| | - A L Goldin
- Department of Microbiology and Molecular Genetics, University of California, Irvine, CA 92697, United States
| | - K Dong
- Department of Entomology and Neuroscience Program, Michigan State University, East Lansing, MI 48824, United States.
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8
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Ojha NK, Nematian-Ardestani E, Neugebauer S, Borowski B, El-Hussein A, Hoshi T, Leipold E, Heinemann SH. Sodium channels as gateable non-photonic sensors for membrane-delimited reactive species. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:1412-9. [PMID: 24513256 DOI: 10.1016/j.bbamem.2014.01.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Revised: 01/24/2014] [Accepted: 01/30/2014] [Indexed: 01/25/2023]
Abstract
Reactive oxygen species (ROS) and reactive oxygen intermediates (ROI) play crucial roles in physiological processes. While excessive ROS damages cells, small fluctuations in ROS levels represent physiological signals important for vital functions. Despite the physiological importance of ROS, many fundamental questions remain unanswered, such as which types of ROS occur in cells, how they distribute inside cells, and how long they remain in an active form. The current study presents a ratiometric sensor of intracellular ROS levels based on genetically engineered voltage-gated sodium channels (roNaV). roNaV can be used for detecting oxidative modification that occurs near the plasma membrane with a sensitivity similar to existing fluorescence-based ROS sensors. Moreover, roNaV has several advantages over traditional sensors because it does not need excitation light for sensing, and thus, can be used to detect phototoxic cellular modifications. In addition, the ROS dynamic range of roNaV is easily manipulated in real time by means of the endogenous channel inactivation mechanism. Measurements on ROS liberated from intracellular Lucifer Yellow and genetically encoded KillerRed have revealed an assessment of ROS lifetime in individual mammalian cells. Flashlight-induced ROS concentration decayed with two major time constants of about 10 and 1000 ms.
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Affiliation(s)
- Navin K Ojha
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany
| | - Ehsan Nematian-Ardestani
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany
| | - Sophie Neugebauer
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany
| | - Benjamin Borowski
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany
| | - Ahmed El-Hussein
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany; The National Institute of Laser Enhanced Science, Cairo University, Cairo, Egypt
| | - Toshinori Hoshi
- Department of Physiology, University of Pennsylvania, Philadelphia, USA
| | - Enrico Leipold
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany
| | - Stefan H Heinemann
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, & Jena University Hospital, Jena, Germany.
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9
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Jones DK, Claydon TW, Ruben PC. Extracellular protons inhibit charge immobilization in the cardiac voltage-gated sodium channel. Biophys J 2014; 105:101-7. [PMID: 23823228 DOI: 10.1016/j.bpj.2013.04.022] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2013] [Revised: 04/10/2013] [Accepted: 04/12/2013] [Indexed: 11/25/2022] Open
Abstract
Low pH depolarizes the voltage-dependence of cardiac voltage-gated sodium (NaV1.5) channel activation and fast inactivation and destabilizes the fast-inactivated state. The molecular basis for these changes in protein behavior has not been reported. We hypothesized that changes in the kinetics of voltage sensor movement may destabilize the fast-inactivated state in NaV1.5. To test this idea, we recorded NaV1.5 gating currents in Xenopus oocytes using a cut-open voltage-clamp with extracellular solution titrated to either pH 7.4 or pH 6.0. Reducing extracellular pH significantly depolarized the voltage-dependence of both the QON/V and QOFF/V curves, and reduced the total charge immobilized during depolarization. We conclude that destabilized fast-inactivation and reduced charge immobilization in NaV1.5 at low pH are functionally related effects.
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Affiliation(s)
- D K Jones
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
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Abstract
The mechanism by which voltage-gated ion channels respond to changes in membrane polarization during action potential signaling in excitable cells has been the subject of research attention since the original description of voltage-dependent sodium and potassium flux in the squid giant axon. The cloning of ion channel genes and the identification of point mutations associated with channelopathy diseases in muscle and brain has facilitated an electrophysiological approach to the study of ion channels. Experimental approaches to the study of voltage gating have incorporated the use of thiosulfonate reagents to test accessibility, fluorescent probes, and toxins to define domain-specific roles of voltage-sensing S4 segments. Crystallography, structural and homology modeling, and molecular dynamics simulations have added computational approaches to study the relationship of channel structure to function. These approaches have tested models of voltage sensor translocation in response to membrane depolarization and incorporate the role of negative countercharges in the S1 to S3 segments to define our present understanding of the mechanism by which the voltage sensor module dictates gating particle permissiveness in excitable cells.
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Affiliation(s)
- James R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID, 83209, USA,
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11
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Jones DK, Ruben PC. Proton modulation of cardiac I Na: a potential arrhythmogenic trigger. Handb Exp Pharmacol 2014; 221:169-81. [PMID: 24737236 DOI: 10.1007/978-3-642-41588-3_8] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Voltage-gated sodium (NaV) channels generate the upstroke and mediate duration of the ventricular action potential, thus they play a critical role in mediating cardiac excitability. Cardiac ischemia triggers extracellular pH to drop as low as pH 6.0, within just 10 min of its onset. Heightened proton concentrations reduce sodium conductance and alter the gating parameters of the cardiac-specific voltage-gated sodium channel, NaV1.5. Most notably, acidosis destabilizes fast inactivation, which plays a critical role in regulating action potential duration. The changes in NaV1.5 channel gating contribute to cardiac dysfunction during ischemia that can cause syncope, cardiac arrhythmia, and even sudden cardiac death. Understanding NaV channel modulation by protons is paramount to treatment and prevention of the deleterious effects of cardiac ischemia and other triggers of cardiac acidosis.
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Sheets MF, Chen T, Hanck DA. Outward stabilization of the voltage sensor in domain II but not domain I speeds inactivation of voltage-gated sodium channels. Am J Physiol Heart Circ Physiol 2013; 305:H1213-21. [DOI: 10.1152/ajpheart.00225.2013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To determine the roles of the individual S4 segments in domains I and II to activation and inactivation kinetics of sodium current ( INa) in NaV1.5, we used a tethered biotin and avidin approach after a site-directed cysteine substitution was made in the second outermost Arg in each S4 (DI-R2C and DII-R2C). We first determined the fraction of gating charge contributed by the individual S4's to maximal gating current (Qmax), and found that the outermost Arg residue in each S4 contributed ∼19% to Qmax with minimal contributions by other arginines. Stabilization of the S4's in DI-R2C and DII-R2C was confirmed by measuring the expected reduction in Qmax. In DI-R2C, stabilization resulted in a decrease in peak INa of ∼45%, while its peak current-voltage ( I-V) and voltage-dependent Na channel availability (SSI) curves were nearly unchanged from wild type (WT). In contrast, stabilization of the DII-R2C enhanced activation with a negative shift in the peak I-V relationship by −7 mV and a larger −17 mV shift in the voltage-dependent SSI curve. Furthermore, its INa decay time constants and time-to-peak INa became more rapid than WT. An explanation for these results is that the depolarized conformation of DII-S4, but not DI-S4, affects the receptor for the inactivation particle formed by the interdomain linker between DIII and IV. In addition, the leftward shifts of both activation and inactivation and the decrease in Gmax after stabilization of the DII-S4 support previous studies that showed β-scorpion toxins trap the voltage sensor of DII in an activated conformation.
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Affiliation(s)
- Michael F. Sheets
- The Nora Eccles Harrison Cardiovascular Research and Training Institute and the Department of Internal Medicine, University of Utah, Salt Lake City, Utah; and
| | - Tiehua Chen
- The Nora Eccles Harrison Cardiovascular Research and Training Institute and the Department of Internal Medicine, University of Utah, Salt Lake City, Utah; and
| | - Dorothy A. Hanck
- The Department of Medicine, The University of Chicago, Chicago, Illinois
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13
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Molecular basis for class Ib anti-arrhythmic inhibition of cardiac sodium channels. Nat Commun 2011; 2:351. [PMID: 21673672 DOI: 10.1038/ncomms1351] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Accepted: 05/12/2011] [Indexed: 12/19/2022] Open
Abstract
Cardiac sodium channels are established therapeutic targets for the management of inherited and acquired arrhythmias by class I anti-arrhythmic drugs (AADs). These drugs share a common target receptor bearing two highly conserved aromatic side chains, and are subdivided by the Vaughan-Williams classification system into classes Ia-c based on their distinct effects on the electrocardiogram. How can these drugs elicit distinct effects on the cardiac action potential by binding to a common receptor? Here we use fluorinated phenylalanine derivatives to test whether the electronegative surface potential of aromatic side chains contributes to inhibition by six class I AADs. Surprisingly, we find that class Ib AADs bind via a strong electrostatic cation-pi interaction, whereas class Ia and Ic AADs rely significantly less on this interaction. Our data shed new light on drug-target interactions underlying the inhibition of cardiac sodium channels by clinically relevant drugs and provide information for the directed design of AADs.
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14
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Sheets MF, Chen T, Hanck DA. Lidocaine partially depolarizes the S4 segment in domain IV of the sodium channel. Pflugers Arch 2010; 461:91-7. [PMID: 20981437 DOI: 10.1007/s00424-010-0894-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 08/10/2010] [Accepted: 10/06/2010] [Indexed: 01/16/2023]
Abstract
Previous studies have shown that lidocaine and other local anesthetic drugs (LAs) cause use-dependent block of sodium current (I (Na)), i.e., block that increases with membrane depolarization by allosteric coupling between drug binding in the inner pore and the S4s in domains III and IV. MTSET protection experiments have established that LAs stabilize DIIIS4 in an outward, depolarized position. Similar tests have not been reported for the DIVS4, although LAs have been shown to reduce DIV's contribution to total gating charge by about one third and to alter its movement such that it contributes more gating charge at negative potentials around -100 mV compared to non-drug-bound sodium (Na) channels. To investigate whether lidocaine reduces the gating charge of DIVS4 by causing it to adopt either a depolarized position at rest or by restricting its outward movement upon depolarization, we performed MTSET protection experiments on I (Na) of the mutant Na channel, R1628C (R3C-DIV), in the presence and absence of 10 mM lidocaine. The results indicate that lidocaine causes the DIVS4 to assume a more depolarized position, which facilitates its movement upon depolarization leading to the excess gating charge at potentials near -100 mV.
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Affiliation(s)
- Michael F Sheets
- The Nora Eccles Harrison Cardiovascular Research & Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112, USA.
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15
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Spencer CI. Actions of ATX-II and other gating-modifiers on Na+ currents in HEK-293 cells expressing WT and ΔKPQ hNaV 1.5 Na+ channels. Toxicon 2009; 53:78-89. [DOI: 10.1016/j.toxicon.2008.10.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Revised: 10/03/2008] [Accepted: 10/16/2008] [Indexed: 11/28/2022]
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16
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Gamal El-Din TM, Grögler D, Lehmann C, Heldstab H, Greeff NG. More gating charges are needed to open a Shaker K+ channel than are needed to open an rBIIA Na+ channel. Biophys J 2008; 95:1165-75. [PMID: 18390620 PMCID: PMC2479606 DOI: 10.1529/biophysj.108.130765] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Accepted: 03/26/2008] [Indexed: 11/18/2022] Open
Abstract
This study presents what is, to our knowledge, a novel technique by means of which the ratio of the single gating charges of voltage-gated rat brain IIA (rBIIA) sodium and Shaker potassium ion channels was estimated. In the experiment, multiple tandems of enhanced green fluorescent protein were constructed and inserted into the C-terminals of Na(+) and K(+) ion channels. cRNA of Na(+) and K(+) ion channels was injected and expressed in Xenopus laevis oocytes. The two electrode voltage-clamp technique allowed us to determine the total gating charge of sodium and potassium ion channels, while a relative measure of the amount of expressed channels could be established on the basis of the quantification of the fluorescence intensity of membrane-bound channels marked by enhanced green fluorescent proteins. As a result, gating charge and fluorescence intensity were found to be positively correlated. A relative comparison of the single gating charges of voltage-gated sodium and potassium ion channels could thus be established: the ratio of the single gating charges of the Shaker potassium channel and the rBIIA sodium channel was found to be 2.5 +/- 0.4. Assuming the single channel gating charge of the Shaker K(+) channel to be approximately 13 elementary charges (well supported by other studies), this leads to approximately six elementary charges for the rBIIA sodium channel, which includes a fraction of gating charge that is missed during inactivation.
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17
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Edgerton GB, Blumenthal KM, Hanck DA. Evidence for multiple effects of ProTxII on activation gating in Na(V)1.5. Toxicon 2008; 52:489-500. [PMID: 18657562 DOI: 10.1016/j.toxicon.2008.06.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2008] [Revised: 06/11/2008] [Accepted: 06/23/2008] [Indexed: 11/26/2022]
Abstract
The peptide toxin ProTxII, recently isolated from the venom of the tarantula spider Thrixopelma pruriens, modifies gating in voltage-gated Na+ and Ca2+ channels. ProTxII is distinct from other known Na+ channel gating modifier toxins in that it affects activation, but not inactivation. It shifts activation gating positively and decreases current magnitude such that the dose-dependence of toxin action measured at a single potential reflects both effects. To test the extent to which these effects were independent, we tracked several different measures of current amplitude, voltage-dependent activation, and current kinetics in Na(V)1.5 in a range of toxin concentrations. Changes in voltage dependence and a decrease in G(max) appeared at relatively low concentrations (40-100 nM) while a positive shift in the voltage range of activation was apparent at higher toxin concentrations (> or =500 nM). Because ProTxII carries a net +4 charge we tested whether electrostatic interactions contributed to toxin action. We examined the effects of ProTxII in the presence of high extracellular Ba2+, known to screen and/or bind to surface charge. Some, but not all aspects of ProTxII modification were sensitive to the presence of Ba2+ indicating the contribution of an electrostatic, surface charge-like mechanism and supporting the idea of a multi-faceted toxin-channel interaction.
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Affiliation(s)
- Gabrielle B Edgerton
- Committee on Neurobiology, University of Chicago, 5841 South Maryland Avenue, MC6094, Chicago, IL 60637, USA
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Groome JR, Dice MC, Fujimoto E, Ruben PC. Charge immobilization of skeletal muscle Na+ channels: role of residues in the inactivation linker. Biophys J 2007; 93:1519-33. [PMID: 17513361 PMCID: PMC1948039 DOI: 10.1529/biophysj.106.102079] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2006] [Accepted: 04/03/2007] [Indexed: 12/18/2022] Open
Abstract
We investigated structural determinants of fast inactivation and deactivation in sodium channels by comparing ionic flux and charge movement in skeletal muscle channels, using mutations of DIII-DIV linker charges. Charge altering and substituting mutations at K-1317, K-1318 depolarized the g(V) curve but hyperpolarized the h(infinity) curve. Charge reversal and substitution at this locus reduced the apparent voltage sensitivity of open- and closed-state fast inactivation. These effects were not observed with charge reversal at E-1314, E-1315. Mutations swapping or neutralizing the negative cluster at 1314, 1315 and the positive cluster at 1317, 1318 indicated that local interactions dictate the coupling of activation to fast inactivation. Gating charge was immobilized before channel entry into fast inactivation in hNa(V)1.4 but to a lesser extent in mutations at K-1317, K-1318. These results suggest that charge is preferentially immobilized in channels inactivating from the open state. Recovery of gating charge proceeded with a single, fast phase in the double mutation K-1317R, K-1318R. This mutation also partially uncoupled recovery from deactivation. Our findings indicate that charged residues near the fast inactivation "particle" allosterically interact with voltage sensors to control aspects of gating in sodium channels.
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Affiliation(s)
- James R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID 83209-8007, USA.
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Sheets MF, Hanck DA. Outward stabilization of the S4 segments in domains III and IV enhances lidocaine block of sodium channels. J Physiol 2007; 582:317-34. [PMID: 17510181 PMCID: PMC2075305 DOI: 10.1113/jphysiol.2007.134262] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The anti-arrhythmic drug lidocaine has been shown to have a lower affinity for block of voltage-gated sodium channels at hyperpolarized potentials compared to depolarized potentials. Concomitantly, lidocaine reduces maximum gating charge (Qmax) by 40% resulting from the complete stabilization of the S4 in domain III in an outward, depolarized position and partial stabilization of the S4 in domain IV in wild-type Na+ channels (Na(V)1.5). To investigate whether the pre-positioning of the S4 segments in these two domains in a depolarized conformation increases affinity for lidocaine block, a cysteine residue was substituted for the 3rd outermost charged residue in the S4 of domain III (R3C-DIII) and for the 2nd outermost Arg in S4 of domain IV (R2C-DIV) in Na(V)1.5. After biotinylation by exposure to extracellular MTSEA-biotin the mutated S4s became stabilized in an outward, depolarized position. For Na+ channels containing both mutations (R3C-DIII + R2C-DIV) the IC50 for rested-state lidocaine block decreased from 194 +/- 15 microM in control to 28 +/- 2 microM after MTSEA-biotin modification. To determine whether an intact inactivation gate (formed by the linker between domains III and IV) was required for local anaesthetic drugs to modify Na+ channel gating currents, a Cys was substituted for the Phe in the IFM motif of the inactivation gate (ICM) and then modified by intracellular MTSET (WT-ICM(MTSET)) before exposure to intracellular QX-222, a quarternary amine. Although WT-ICM(MTSET) required higher concentrations of drug to block I(Na) compared to WT, Qmax decreased by 35% and the V1/2 shifted leftward as previously demonstrated for WT. The effect of stabilization of the S4s in domains III and IV in the absence of an intact inactivation gate on lidocaine block was determined for R3C-DIII + ICM, R2C-DIV + ICM and R3C-DIII + R2C-DIV + ICM, and compared to WT-ICM. IC50 values were 1360 +/- 430 microM, 890 +/- 70 microM, 670 +/- 30 microM and 1920 +/- 60 microM, respectively. Thermodynamic mutant-cycle analysis was consistent with additive (i.e. independent) contributions from stabilization of the individual S4s in R3C-DIII + ICM and R2C-DIV + ICM. We conclude that the positions of the S4s in domains III and IV are major determinants of the voltage dependence of lidocaine affinity.
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Affiliation(s)
- Michael F Sheets
- The Nora Eccles Harrison Cardiovascular Research & Training Institute and Department of Internal Medicine, University of Utah, Salt Lake City, UT 84112, USA.
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Groome JR, Alexander HM, Fujimoto E, Sherry M, Petty D. Central Charged Residues in DIIIS4 Regulate Deactivation Gating in Skeletal Muscle Sodium Channels. Cell Mol Neurobiol 2006; 27:87-106. [PMID: 17151947 DOI: 10.1007/s10571-006-9120-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2006] [Accepted: 09/11/2006] [Indexed: 10/23/2022]
Abstract
1. Mutations in the S4 segment of domain III in the voltage gated skeletal muscle sodium channel hNa(V)1.4 were constructed to test the roles of each charged residue in deactivation gating. Mutations comprised charge reversals at K1-R6, charge neutralization, and substitution at R4 and R5. 2. Charge-reversing mutations at R4 and R5 produced the greatest alteration of activation parameters compared to hNa(V)1.4. Effects included depolarization of the conductance/voltage (g/V) curve, decreased valence and slowing of kinetics. 3. Reversal of charge at R2 to R4 hyperpolarized, and reversal at R5 or R6 depolarized the h (infinity) curve. Most DIIIS4 mutations slowed inactivation from the open state. R4E slowed closed state fast inactivation and R5E inhibited its completion .4. Deactivation from the open and/or inactivated state was prolonged in mutations reversing charge at R2 to R4 but accelerated by reversal of charge at R5 or R6. Effects were most pronounced at central charges R4 and R5. 5. Charge and structure each contribute to effects of mutations at R4 and R5 on channel gating. Effects of mutations on activation and deactivation at R4 and, to a lesser extent R5, were primarily owing to charge alteration, whereas effects on fast inactivation were charge independent.
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Affiliation(s)
- James R Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID 83204, USA.
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Zhu Y, Kyle JW, Lee PJ. Flecainide sensitivity of a Na channel long QT mutation shows an open-channel blocking mechanism for use-dependent block. Am J Physiol Heart Circ Physiol 2006; 291:H29-37. [PMID: 16501012 DOI: 10.1152/ajpheart.01317.2005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
A long QT mutation in the cardiac sodium channel, D1790G (DG), shows enhanced flecainide use-dependent block (UDB). The relative importance of open and inactivated states of the channel in flecainide UDB has been controversial. We used a modifiable, inactivation-deficient mutant channel that contains the F1486C mutation in the IFM motif to investigate the UDB difference between the wild-type (WT-ICM) and DG (DG-ICM) channels. UDB at 5 Hz was greater in DG-ICM than WT-ICM, and IC50 values for steady-state UDB were 7.19 and 18.06 microM, respectively. When [2-(trimethyammonium) ethyl]methanethiosulfonate bromide (MTSET) was included in the pipette and fast inactivation was disabled, IC50 was 5.04 microM for DG-ICM and 12.63 microM for WT-ICM. We measured open-channel block by flecainide directly in MTSET-treated, noninactivating ICM channels. Steady-state block was higher for DG-ICM than WT-ICM (IC50 was 2.34 microM for DG-ICM and 5.87 microM for WT-ICM), suggesting that open-channel block is an important determinant of flecainide UDB. We obtained association (kon) and dissociation (koff) rates for open-channel block by the Langmuir-isotherm model. They were koff = 31.37 s(-1), kon = 5.83 s(-1).microM(-1), and calculated Kd = 5.38 microM for WT-ICM (where Kd = koff/kon); and koff = 24.88 s(-1), kon = 9.54 s(-1).microM(-1), and calculated Kd = 2.61 microM for DG-ICM. These Kd values were similar to IC50 measured from steady-state open-channel block. Furthermore, we modeled UDB mathematically by using these kinetic rates and found that the model predicted experimental UDB accurately. The recovery from UDB had a minor contribution to UDB. Flecainide UDB is predominantly determined by an open-channel blocking mechanism, and DG-ICM channels appeared to have an altered open-channel state with higher flecainide affinity than WT-ICM.
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Affiliation(s)
- Yujie Zhu
- Department of Medicine and Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, IL 60612, USA
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