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Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation

The primary voltage sensor of the sodium channel is comprised of four positively charged S4 segments that mainly differ in the number of charged residues and are expected to contribute differentially to the gating process. To understand their kinetic and steady-state behavior, the fluorescence signa...

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Autores principales: Chanda, Baron, Bezanilla, Francisco
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 2002
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229551/
https://www.ncbi.nlm.nih.gov/pubmed/12407076
http://dx.doi.org/10.1085/jgp.20028679
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author Chanda, Baron
Bezanilla, Francisco
author_facet Chanda, Baron
Bezanilla, Francisco
author_sort Chanda, Baron
collection PubMed
description The primary voltage sensor of the sodium channel is comprised of four positively charged S4 segments that mainly differ in the number of charged residues and are expected to contribute differentially to the gating process. To understand their kinetic and steady-state behavior, the fluorescence signals from the sites proximal to each of the four S4 segments of a rat skeletal muscle sodium channel were monitored simultaneously with either gating or ionic currents. At least one of the kinetic components of fluorescence from every S4 segment correlates with movement of gating charge. The fast kinetic component of fluorescence from sites S216C (S4 domain I), S660C (S4 domain II), and L1115C (S4 domain III) is comparable to the fast component of gating currents. In contrast, the fast component of fluorescence from the site S1436C (S4 domain IV) correlates with the slow component of gating. In all the cases, the slow component of fluorescence does not have any apparent correlation with charge movement. The fluorescence signals from sites reflecting the movement of S4s in the first three domains initiate simultaneously, whereas the fluorescence signals from the site S1436C exhibit a lag phase. These results suggest that the voltage-dependent movement of S4 domain IV is a later step in the activation sequence. Analysis of equilibrium and kinetic properties of fluorescence over activation voltage range indicate that S4 domain III is likely to move at most hyperpolarized potentials, whereas the S4s in domain I and domain II move at more depolarized potentials. The kinetics of fluorescence changes from sites near S4-DIV are slower than the activation time constants, suggesting that the voltage-dependent movement of S4-DIV may not be a prerequisite for channel opening. These experiments allow us to map structural features onto the kinetic landscape of a sodium channel during activation.
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spelling pubmed-22295512008-04-16 Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation Chanda, Baron Bezanilla, Francisco J Gen Physiol Article The primary voltage sensor of the sodium channel is comprised of four positively charged S4 segments that mainly differ in the number of charged residues and are expected to contribute differentially to the gating process. To understand their kinetic and steady-state behavior, the fluorescence signals from the sites proximal to each of the four S4 segments of a rat skeletal muscle sodium channel were monitored simultaneously with either gating or ionic currents. At least one of the kinetic components of fluorescence from every S4 segment correlates with movement of gating charge. The fast kinetic component of fluorescence from sites S216C (S4 domain I), S660C (S4 domain II), and L1115C (S4 domain III) is comparable to the fast component of gating currents. In contrast, the fast component of fluorescence from the site S1436C (S4 domain IV) correlates with the slow component of gating. In all the cases, the slow component of fluorescence does not have any apparent correlation with charge movement. The fluorescence signals from sites reflecting the movement of S4s in the first three domains initiate simultaneously, whereas the fluorescence signals from the site S1436C exhibit a lag phase. These results suggest that the voltage-dependent movement of S4 domain IV is a later step in the activation sequence. Analysis of equilibrium and kinetic properties of fluorescence over activation voltage range indicate that S4 domain III is likely to move at most hyperpolarized potentials, whereas the S4s in domain I and domain II move at more depolarized potentials. The kinetics of fluorescence changes from sites near S4-DIV are slower than the activation time constants, suggesting that the voltage-dependent movement of S4-DIV may not be a prerequisite for channel opening. These experiments allow us to map structural features onto the kinetic landscape of a sodium channel during activation. The Rockefeller University Press 2002-11 /pmc/articles/PMC2229551/ /pubmed/12407076 http://dx.doi.org/10.1085/jgp.20028679 Text en Copyright © 2002, The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Article
Chanda, Baron
Bezanilla, Francisco
Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title_full Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title_fullStr Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title_full_unstemmed Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title_short Tracking Voltage-dependent Conformational Changes in Skeletal Muscle Sodium Channel during Activation
title_sort tracking voltage-dependent conformational changes in skeletal muscle sodium channel during activation
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229551/
https://www.ncbi.nlm.nih.gov/pubmed/12407076
http://dx.doi.org/10.1085/jgp.20028679
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