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Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels
Tetrodotoxin-resistant (TTX-R) Na(+) channels are 1,000-fold less sensitive to TTX than TTX-sensitive (TTX-S) Na(+) channels. On the other hand, TTX-R channels are much more susceptible to external Cd(2+) block than TTX-S channels. A cysteine (or serine) residue situated just next to the aspartate r...
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
2002
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2234463/ https://www.ncbi.nlm.nih.gov/pubmed/12149278 http://dx.doi.org/10.1085/jgp.20018536 |
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author | Kuo, Chung-Chin Lin, Ting-Jiun Hsieh, Chi-Pan |
author_facet | Kuo, Chung-Chin Lin, Ting-Jiun Hsieh, Chi-Pan |
author_sort | Kuo, Chung-Chin |
collection | PubMed |
description | Tetrodotoxin-resistant (TTX-R) Na(+) channels are 1,000-fold less sensitive to TTX than TTX-sensitive (TTX-S) Na(+) channels. On the other hand, TTX-R channels are much more susceptible to external Cd(2+) block than TTX-S channels. A cysteine (or serine) residue situated just next to the aspartate residue of the presumable selectivity filter “DEKA” ring of the TTX-R channel has been identified as the key ligand determining the binding affinity of both TTX and Cd(2+). In this study we demonstrate that the binding affinity of Cd(2+) to the TTX-R channels in neurons from dorsal root ganglia has little intrinsic voltage dependence, but is significantly influenced by the direction of Na(+) current flow. In the presence of inward Na(+) current, the apparent dissociation constant of Cd(2+) (∼200 μM) is ∼9 times smaller than that in the presence of outward Na(+) current. The Na(+) flow–dependent binding affinity change of Cd(2+) block is true no matter whether the direction of Na(+) current is secured by asymmetrical chemical gradient (e.g., 150 mM Na(+) vs. 150 mM Cs(+) on different sides of the membrane, 0 mV) or by asymmetrical electrical gradient (e.g., 150 mM Na(+) on both sides of the membrane, −20 mV vs. 20 mV). These findings suggest that Cd(2+) is a pore blocker of TTX-R channels with its binding site located in a multiion, single-file region near the external pore mouth. Quantitative analysis of the flow dependence with the flux-coupling equation reveals that at least two Na(+) ions coexist with the blocking Cd(2+) ion in this pore region in the presence of 150 mM ambient Na(+). Thus, the selectivity filter of the TTX-R Na(+) channels in dorsal root ganglion neurons might be located in or close to a multiion single-file pore segment connected externally to a wide vestibule, a molecular feature probably shared by other voltage-gated cationic channels, such as some Ca(2+) and K(+) channels. |
format | Text |
id | pubmed-2234463 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2002 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22344632008-04-16 Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels Kuo, Chung-Chin Lin, Ting-Jiun Hsieh, Chi-Pan J Gen Physiol Article Tetrodotoxin-resistant (TTX-R) Na(+) channels are 1,000-fold less sensitive to TTX than TTX-sensitive (TTX-S) Na(+) channels. On the other hand, TTX-R channels are much more susceptible to external Cd(2+) block than TTX-S channels. A cysteine (or serine) residue situated just next to the aspartate residue of the presumable selectivity filter “DEKA” ring of the TTX-R channel has been identified as the key ligand determining the binding affinity of both TTX and Cd(2+). In this study we demonstrate that the binding affinity of Cd(2+) to the TTX-R channels in neurons from dorsal root ganglia has little intrinsic voltage dependence, but is significantly influenced by the direction of Na(+) current flow. In the presence of inward Na(+) current, the apparent dissociation constant of Cd(2+) (∼200 μM) is ∼9 times smaller than that in the presence of outward Na(+) current. The Na(+) flow–dependent binding affinity change of Cd(2+) block is true no matter whether the direction of Na(+) current is secured by asymmetrical chemical gradient (e.g., 150 mM Na(+) vs. 150 mM Cs(+) on different sides of the membrane, 0 mV) or by asymmetrical electrical gradient (e.g., 150 mM Na(+) on both sides of the membrane, −20 mV vs. 20 mV). These findings suggest that Cd(2+) is a pore blocker of TTX-R channels with its binding site located in a multiion, single-file region near the external pore mouth. Quantitative analysis of the flow dependence with the flux-coupling equation reveals that at least two Na(+) ions coexist with the blocking Cd(2+) ion in this pore region in the presence of 150 mM ambient Na(+). Thus, the selectivity filter of the TTX-R Na(+) channels in dorsal root ganglion neurons might be located in or close to a multiion single-file pore segment connected externally to a wide vestibule, a molecular feature probably shared by other voltage-gated cationic channels, such as some Ca(2+) and K(+) channels. The Rockefeller University Press 2002-08 /pmc/articles/PMC2234463/ /pubmed/12149278 http://dx.doi.org/10.1085/jgp.20018536 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 Kuo, Chung-Chin Lin, Ting-Jiun Hsieh, Chi-Pan Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title | Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title_full | Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title_fullStr | Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title_full_unstemmed | Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title_short | Effect of Na(+) Flow on Cd(2+) Block of Tetrodotoxin-resistant Na(+) Channels |
title_sort | effect of na(+) flow on cd(2+) block of tetrodotoxin-resistant na(+) channels |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2234463/ https://www.ncbi.nlm.nih.gov/pubmed/12149278 http://dx.doi.org/10.1085/jgp.20018536 |
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