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The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors

The α(1)β(2)γ(2) and α(3)β(3)γ(2) are two isoforms of γ-aminobutyric acid type A (GABA(A)) receptor that are widely distributed in the brain. Both are found at synapses, for example in the thalamus, where they mediate distinctly different inhibitory postsynaptic current profiles, particularly with r...

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Autores principales: Keramidas, Angelo, Harrison, Neil L.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 2010
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2806416/
https://www.ncbi.nlm.nih.gov/pubmed/20038526
http://dx.doi.org/10.1085/jgp.200910317
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author Keramidas, Angelo
Harrison, Neil L.
author_facet Keramidas, Angelo
Harrison, Neil L.
author_sort Keramidas, Angelo
collection PubMed
description The α(1)β(2)γ(2) and α(3)β(3)γ(2) are two isoforms of γ-aminobutyric acid type A (GABA(A)) receptor that are widely distributed in the brain. Both are found at synapses, for example in the thalamus, where they mediate distinctly different inhibitory postsynaptic current profiles, particularly with respect to decay time. The two isoforms were expressed in HEK293 cells, and single-channel activity was recorded from outside-out patches. The kinetic characteristics of both isoforms were investigated by analyzing single-channel currents over a wide range of GABA concentrations. α(1)β(2)γ(2) channels exhibited briefer active periods than α(3)β(3)γ(2) channels over the entire range of agonist concentrations and had lower intraburst open probabilities at subsaturating concentrations. Activation mechanisms were constructed by fitting postulated schemes to data recorded at saturating and subsaturating GABA concentrations simultaneously. Reaction mechanisms were ranked according to log-likelihood values and how accurately they simulated ensemble currents. The highest ranked mechanism for both channels consisted of two sequential binding steps, followed by three conducting and three nonconducting configurations. The equilibrium dissociation constant for GABA at α(3)β(3)γ(2) channels was ∼2.6 µM compared with ∼19 µM for α(1)β(2)γ(2) channels, suggesting that GABA binds to the α(3)β(3)γ(2) channels with higher affinity. A notable feature of the mechanism was that two consecutive doubly liganded shut states preceded all three open configurations. The lifetime of the third shut state was briefer for the α(3)β(3)γ(2) channels. The longer active periods, higher affinity, and preference for conducting states are consistent with the slower decay of inhibitory currents at synapses that contain α(3)β(3)γ(2) channels. The reaction mechanism we describe here may also be appropriate for the analysis of other types of GABA(A) receptors and provides a framework for rational investigation of the kinetic effects of a variety of therapeutic agents that activate or modulate GABA(A) receptors and hence influence synaptic and extrasynaptic inhibition in the central nervous system.
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spelling pubmed-28064162010-07-01 The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors Keramidas, Angelo Harrison, Neil L. J Gen Physiol Article The α(1)β(2)γ(2) and α(3)β(3)γ(2) are two isoforms of γ-aminobutyric acid type A (GABA(A)) receptor that are widely distributed in the brain. Both are found at synapses, for example in the thalamus, where they mediate distinctly different inhibitory postsynaptic current profiles, particularly with respect to decay time. The two isoforms were expressed in HEK293 cells, and single-channel activity was recorded from outside-out patches. The kinetic characteristics of both isoforms were investigated by analyzing single-channel currents over a wide range of GABA concentrations. α(1)β(2)γ(2) channels exhibited briefer active periods than α(3)β(3)γ(2) channels over the entire range of agonist concentrations and had lower intraburst open probabilities at subsaturating concentrations. Activation mechanisms were constructed by fitting postulated schemes to data recorded at saturating and subsaturating GABA concentrations simultaneously. Reaction mechanisms were ranked according to log-likelihood values and how accurately they simulated ensemble currents. The highest ranked mechanism for both channels consisted of two sequential binding steps, followed by three conducting and three nonconducting configurations. The equilibrium dissociation constant for GABA at α(3)β(3)γ(2) channels was ∼2.6 µM compared with ∼19 µM for α(1)β(2)γ(2) channels, suggesting that GABA binds to the α(3)β(3)γ(2) channels with higher affinity. A notable feature of the mechanism was that two consecutive doubly liganded shut states preceded all three open configurations. The lifetime of the third shut state was briefer for the α(3)β(3)γ(2) channels. The longer active periods, higher affinity, and preference for conducting states are consistent with the slower decay of inhibitory currents at synapses that contain α(3)β(3)γ(2) channels. The reaction mechanism we describe here may also be appropriate for the analysis of other types of GABA(A) receptors and provides a framework for rational investigation of the kinetic effects of a variety of therapeutic agents that activate or modulate GABA(A) receptors and hence influence synaptic and extrasynaptic inhibition in the central nervous system. The Rockefeller University Press 2010-01 /pmc/articles/PMC2806416/ /pubmed/20038526 http://dx.doi.org/10.1085/jgp.200910317 Text en © 2009 Keramidas and Harrison 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.jgp.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).
spellingShingle Article
Keramidas, Angelo
Harrison, Neil L.
The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title_full The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title_fullStr The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title_full_unstemmed The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title_short The activation mechanism of α(1)β(2)γ(2S) and α(3)β(3)γ(2S) GABA(A) receptors
title_sort activation mechanism of α(1)β(2)γ(2s) and α(3)β(3)γ(2s) gaba(a) receptors
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2806416/
https://www.ncbi.nlm.nih.gov/pubmed/20038526
http://dx.doi.org/10.1085/jgp.200910317
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