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Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)

Large quaternary ammonium (QA) ions block voltage-gated K(+) (Kv) channels by binding with a 1:1 stoichiometry in an aqueous cavity that is exposed to the cytoplasm only when channels are open. S-nitrosodithiothreitol (SNDTT; ONSCH(2)CH(OH)CH(OH)CH(2)SNO) produces qualitatively similar “open-channel...

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Detalles Bibliográficos
Autores principales: Brock, Mathew W., Mathes, Chris, Gilly, William F.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 2001
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2233744/
https://www.ncbi.nlm.nih.gov/pubmed/11429448
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author Brock, Mathew W.
Mathes, Chris
Gilly, William F.
author_facet Brock, Mathew W.
Mathes, Chris
Gilly, William F.
author_sort Brock, Mathew W.
collection PubMed
description Large quaternary ammonium (QA) ions block voltage-gated K(+) (Kv) channels by binding with a 1:1 stoichiometry in an aqueous cavity that is exposed to the cytoplasm only when channels are open. S-nitrosodithiothreitol (SNDTT; ONSCH(2)CH(OH)CH(OH)CH(2)SNO) produces qualitatively similar “open-channel block” in Kv channels despite a radically different structure. SNDTT is small, electrically neutral, and not very hydrophobic. In whole-cell voltage-clamped squid giant fiber lobe neurons, bath-applied SNDTT causes reversible time-dependent block of Kv channels, but not Na(+) or Ca(2)+ channels. Inactivation-removed ShakerB (ShBΔ) Kv1 channels expressed in HEK 293 cells are similarly blocked and were used to study further the action of SNDTT. Dose–response data are consistent with a scheme in which two SNDTT molecules bind sequentially to a single channel, with binding of the first being sufficient to produce block. The dissociation constant for the binding of the second SNDTT molecule (K (d2) = 0.14 mM) is lower than that of the first molecule (K (d1) = 0.67 mM), indicating cooperativity. The half-blocking concentration (K (1/2)) is ∼0.2 mM. Steady-state block by this electrically neutral compound has a voltage dependence (about −0.3 e(0)) similar in magnitude but opposite in directionality to that reported for QA ions. Both nitrosyl groups on SNDTT (one on each sulfur atom) are required for block, but transfer of these reactive groups to channel cysteine residues is not involved. SNDTT undergoes a slow intramolecular reaction (τ ≈ 770 s) in which these NO groups are liberated, leading to spontaneous reversal of the SNDTT effect. Competition with internal tetraethylammonium indicates that bath-applied SNDTT crosses the cell membrane to act at an internal site, most likely within the channel cavity. Finally, SNDTT is remarkably selective for Kv1 channels. When individually expressed in HEK 293 cells, rat Kv1.1–1.6 display profound time-dependent block by SNDTT, an effect not seen for Kv2.1, 3.1b, or 4.2.
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spelling pubmed-22337442008-04-22 Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt) Brock, Mathew W. Mathes, Chris Gilly, William F. J Gen Physiol Original Article Large quaternary ammonium (QA) ions block voltage-gated K(+) (Kv) channels by binding with a 1:1 stoichiometry in an aqueous cavity that is exposed to the cytoplasm only when channels are open. S-nitrosodithiothreitol (SNDTT; ONSCH(2)CH(OH)CH(OH)CH(2)SNO) produces qualitatively similar “open-channel block” in Kv channels despite a radically different structure. SNDTT is small, electrically neutral, and not very hydrophobic. In whole-cell voltage-clamped squid giant fiber lobe neurons, bath-applied SNDTT causes reversible time-dependent block of Kv channels, but not Na(+) or Ca(2)+ channels. Inactivation-removed ShakerB (ShBΔ) Kv1 channels expressed in HEK 293 cells are similarly blocked and were used to study further the action of SNDTT. Dose–response data are consistent with a scheme in which two SNDTT molecules bind sequentially to a single channel, with binding of the first being sufficient to produce block. The dissociation constant for the binding of the second SNDTT molecule (K (d2) = 0.14 mM) is lower than that of the first molecule (K (d1) = 0.67 mM), indicating cooperativity. The half-blocking concentration (K (1/2)) is ∼0.2 mM. Steady-state block by this electrically neutral compound has a voltage dependence (about −0.3 e(0)) similar in magnitude but opposite in directionality to that reported for QA ions. Both nitrosyl groups on SNDTT (one on each sulfur atom) are required for block, but transfer of these reactive groups to channel cysteine residues is not involved. SNDTT undergoes a slow intramolecular reaction (τ ≈ 770 s) in which these NO groups are liberated, leading to spontaneous reversal of the SNDTT effect. Competition with internal tetraethylammonium indicates that bath-applied SNDTT crosses the cell membrane to act at an internal site, most likely within the channel cavity. Finally, SNDTT is remarkably selective for Kv1 channels. When individually expressed in HEK 293 cells, rat Kv1.1–1.6 display profound time-dependent block by SNDTT, an effect not seen for Kv2.1, 3.1b, or 4.2. The Rockefeller University Press 2001-07-01 /pmc/articles/PMC2233744/ /pubmed/11429448 Text en © 2001 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 Original Article
Brock, Mathew W.
Mathes, Chris
Gilly, William F.
Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title_full Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title_fullStr Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title_full_unstemmed Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title_short Selective Open-Channel Block of Shaker (Kv1) Potassium Channels by S-Nitrosodithiothreitol (Sndtt)
title_sort selective open-channel block of shaker (kv1) potassium channels by s-nitrosodithiothreitol (sndtt)
topic Original Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2233744/
https://www.ncbi.nlm.nih.gov/pubmed/11429448
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