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Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation

It has been shown that β auxiliary subunits increase current amplitude in voltage-dependent calcium channels. In this study, however, we found a novel inhibitory effect of β3 subunit on macroscopic Ba(2+) currents through recombinant N- and R-type calcium channels expressed in Xenopus oocytes. Overe...

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Autores principales: Yasuda, Takahiro, Lewis, Richard J., Adams, David J.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 2004
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2217459/
https://www.ncbi.nlm.nih.gov/pubmed/15024042
http://dx.doi.org/10.1085/jgp.200308967
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author Yasuda, Takahiro
Lewis, Richard J.
Adams, David J.
author_facet Yasuda, Takahiro
Lewis, Richard J.
Adams, David J.
author_sort Yasuda, Takahiro
collection PubMed
description It has been shown that β auxiliary subunits increase current amplitude in voltage-dependent calcium channels. In this study, however, we found a novel inhibitory effect of β3 subunit on macroscopic Ba(2+) currents through recombinant N- and R-type calcium channels expressed in Xenopus oocytes. Overexpressed β3 (12.5 ng/cell cRNA) significantly suppressed N- and R-type, but not L-type, calcium channel currents at “physiological” holding potentials (HPs) of −60 and −80 mV. At a HP of −80 mV, coinjection of various concentrations (0–12.5 ng) of the β3 with Ca(v)2.2α(1) and α(2)δ enhanced the maximum conductance of expressed channels at lower β3 concentrations but at higher concentrations (>2.5 ng/cell) caused a marked inhibition. The β3-induced current suppression was reversed at a HP of −120 mV, suggesting that the inhibition was voltage dependent. A high concentration of Ba(2+) (40 mM) as a charge carrier also largely diminished the effect of β3 at −80 mV. Therefore, experimental conditions (HP, divalent cation concentration, and β3 subunit concentration) approaching normal physiological conditions were critical to elucidate the full extent of this novel β3 effect. Steady-state inactivation curves revealed that N-type channels exhibited “closed-state” inactivation without β3, and that β3 caused an ∼40-mV negative shift of the inactivation, producing a second component with an inactivation midpoint of approximately −85 mV. The inactivation of N-type channels in the presence of a high concentration (12.5 ng/cell) of β3 developed slowly and the time-dependent inactivation curve was best fit by the sum of two exponential functions with time constants of 14 s and 8.8 min at −80 mV. Similar “ultra-slow” inactivation was observed for N-type channels without β3. Thus, β3 can have a profound negative regulatory effect on N-type (and also R-type) calcium channels by causing a hyperpolarizing shift of the inactivation without affecting “ultra-slow” and “closed-state” inactivation properties.
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spelling pubmed-22174592008-03-21 Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation Yasuda, Takahiro Lewis, Richard J. Adams, David J. J Gen Physiol Article It has been shown that β auxiliary subunits increase current amplitude in voltage-dependent calcium channels. In this study, however, we found a novel inhibitory effect of β3 subunit on macroscopic Ba(2+) currents through recombinant N- and R-type calcium channels expressed in Xenopus oocytes. Overexpressed β3 (12.5 ng/cell cRNA) significantly suppressed N- and R-type, but not L-type, calcium channel currents at “physiological” holding potentials (HPs) of −60 and −80 mV. At a HP of −80 mV, coinjection of various concentrations (0–12.5 ng) of the β3 with Ca(v)2.2α(1) and α(2)δ enhanced the maximum conductance of expressed channels at lower β3 concentrations but at higher concentrations (>2.5 ng/cell) caused a marked inhibition. The β3-induced current suppression was reversed at a HP of −120 mV, suggesting that the inhibition was voltage dependent. A high concentration of Ba(2+) (40 mM) as a charge carrier also largely diminished the effect of β3 at −80 mV. Therefore, experimental conditions (HP, divalent cation concentration, and β3 subunit concentration) approaching normal physiological conditions were critical to elucidate the full extent of this novel β3 effect. Steady-state inactivation curves revealed that N-type channels exhibited “closed-state” inactivation without β3, and that β3 caused an ∼40-mV negative shift of the inactivation, producing a second component with an inactivation midpoint of approximately −85 mV. The inactivation of N-type channels in the presence of a high concentration (12.5 ng/cell) of β3 developed slowly and the time-dependent inactivation curve was best fit by the sum of two exponential functions with time constants of 14 s and 8.8 min at −80 mV. Similar “ultra-slow” inactivation was observed for N-type channels without β3. Thus, β3 can have a profound negative regulatory effect on N-type (and also R-type) calcium channels by causing a hyperpolarizing shift of the inactivation without affecting “ultra-slow” and “closed-state” inactivation properties. The Rockefeller University Press 2004-04 /pmc/articles/PMC2217459/ /pubmed/15024042 http://dx.doi.org/10.1085/jgp.200308967 Text en Copyright © 2004, 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
Yasuda, Takahiro
Lewis, Richard J.
Adams, David J.
Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title_full Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title_fullStr Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title_full_unstemmed Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title_short Overexpressed Ca(v)β3 Inhibits N-type (Ca(v)2.2) Calcium Channel Currents through a Hyperpolarizing Shift of “Ultra-slow” and “Closed-state” Inactivation
title_sort overexpressed ca(v)β3 inhibits n-type (ca(v)2.2) calcium channel currents through a hyperpolarizing shift of “ultra-slow” and “closed-state” inactivation
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2217459/
https://www.ncbi.nlm.nih.gov/pubmed/15024042
http://dx.doi.org/10.1085/jgp.200308967
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