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State-independent Block of BK Channels by an Intracellular Quaternary Ammonium
Intracellular blockade by quaternary ammonium (QA) molecules of many potassium channels is state dependent, where the requirement for channel opening is evidenced by a time-dependent component of block in the macroscopic record. Whether this is the case for Ca(2+)- and voltage-activated potassium (B...
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
2006
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2151567/ https://www.ncbi.nlm.nih.gov/pubmed/16940557 http://dx.doi.org/10.1085/jgp.200609579 |
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author | Wilkens, Christina M. Aldrich, Richard W. |
author_facet | Wilkens, Christina M. Aldrich, Richard W. |
author_sort | Wilkens, Christina M. |
collection | PubMed |
description | Intracellular blockade by quaternary ammonium (QA) molecules of many potassium channels is state dependent, where the requirement for channel opening is evidenced by a time-dependent component of block in the macroscopic record. Whether this is the case for Ca(2+)- and voltage-activated potassium (BK) channels, however, remains unclear. Previous work (Li, W., and R.W. Aldrich. 2004. J. Gen. Physiol. 124:43–57) tentatively proposed a state-dependent, trapping model, but left open the possibility of state-independent block. Here, we found BK channel blockade by a novel QA derivative, bbTBA, was time dependent, raising the possibility of state-dependent, open channel block. Alternatively, the observed voltage dependence of block could be sufficient to explain time-dependent block. We have used steady-state and kinetic measurements of bbTBA blockade in order to discriminate between these two possibilities. bbTBA did not significantly slow deactivation kinetics at potentials between −200 and −100 mV, suggesting that channels can close unhindered by bound bbTBA. We further find no evidence that bbTBA is trapped inside BK channels after closing. Measurements of steady state fractional block at +40 mV revealed a 1.3-fold change in apparent affinity for a 33-fold change in P(o), in striking contrast to the 31-fold change predicted by state-dependent block. Finally, the appearance of a third kinetic component of bbTBA blockade at high concentrations is incompatible with state-dependent block. Our results suggest that access of intracellular bbTBA to the BK channel cavity is not strictly gated by channel opening and closing, and imply that the permeation gate for BK channels may not be intracellular. |
format | Text |
id | pubmed-2151567 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2006 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-21515672008-01-17 State-independent Block of BK Channels by an Intracellular Quaternary Ammonium Wilkens, Christina M. Aldrich, Richard W. J Gen Physiol Articles Intracellular blockade by quaternary ammonium (QA) molecules of many potassium channels is state dependent, where the requirement for channel opening is evidenced by a time-dependent component of block in the macroscopic record. Whether this is the case for Ca(2+)- and voltage-activated potassium (BK) channels, however, remains unclear. Previous work (Li, W., and R.W. Aldrich. 2004. J. Gen. Physiol. 124:43–57) tentatively proposed a state-dependent, trapping model, but left open the possibility of state-independent block. Here, we found BK channel blockade by a novel QA derivative, bbTBA, was time dependent, raising the possibility of state-dependent, open channel block. Alternatively, the observed voltage dependence of block could be sufficient to explain time-dependent block. We have used steady-state and kinetic measurements of bbTBA blockade in order to discriminate between these two possibilities. bbTBA did not significantly slow deactivation kinetics at potentials between −200 and −100 mV, suggesting that channels can close unhindered by bound bbTBA. We further find no evidence that bbTBA is trapped inside BK channels after closing. Measurements of steady state fractional block at +40 mV revealed a 1.3-fold change in apparent affinity for a 33-fold change in P(o), in striking contrast to the 31-fold change predicted by state-dependent block. Finally, the appearance of a third kinetic component of bbTBA blockade at high concentrations is incompatible with state-dependent block. Our results suggest that access of intracellular bbTBA to the BK channel cavity is not strictly gated by channel opening and closing, and imply that the permeation gate for BK channels may not be intracellular. The Rockefeller University Press 2006-09 /pmc/articles/PMC2151567/ /pubmed/16940557 http://dx.doi.org/10.1085/jgp.200609579 Text en Copyright © 2006, 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 | Articles Wilkens, Christina M. Aldrich, Richard W. State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title | State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title_full | State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title_fullStr | State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title_full_unstemmed | State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title_short | State-independent Block of BK Channels by an Intracellular Quaternary Ammonium |
title_sort | state-independent block of bk channels by an intracellular quaternary ammonium |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2151567/ https://www.ncbi.nlm.nih.gov/pubmed/16940557 http://dx.doi.org/10.1085/jgp.200609579 |
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