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Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes

The ability of acetylcholine (ACh) to inhibit beta-agonist stimulated calcium current was compared to its ability to activate the inwardly rectifying potassium current IK(ACh) in frog atrial myocytes. As suggested by previous studies, ACh inhibited the calcium current at concentrations (EC50 = 8 nM)...

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Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1994
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229240/
https://www.ncbi.nlm.nih.gov/pubmed/7876829
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description The ability of acetylcholine (ACh) to inhibit beta-agonist stimulated calcium current was compared to its ability to activate the inwardly rectifying potassium current IK(ACh) in frog atrial myocytes. As suggested by previous studies, ACh inhibited the calcium current at concentrations (EC50 = 8 nM) significantly lower than those required for the activation of IK(ACh) (EC50 = 101 nM). The pharmacological profiles of the two responses suggest that despite the differences in agonist sensitivity, both are mediated by the same (m2) type of muscarinic receptors. Intracellular application of GDP beta S, an inhibitor of G protein function, completely abolished both responses, implying that both actions of ACh are coupled to effectors by G proteins. In contrast, intracellular application of pertussis toxin (PTX) shifted to higher concentrations (EC50 = 170 nM) but did not abolish inhibition of the calcium current by ACh even though the block of the IK(ACh) response was complete. Increasingly large PTX concentrations and/or prolonged PTX treatments revealed a limiting, PTX- resistant inhibitory component that appears to be mediated by a PTX- insensitive G protein distinct from that mediating IK(ACh). For the PTX- sensitive components, the different agonist dependencies of IK(ACh) activation and calcium current inhibition may imply that different G proteins mediate each response although alternate possibilities involving the same G protein either functionally sequestered and/or differentially affected by interactions with effectors, can not be ruled out.
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spelling pubmed-22292402008-04-23 Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes J Gen Physiol Articles The ability of acetylcholine (ACh) to inhibit beta-agonist stimulated calcium current was compared to its ability to activate the inwardly rectifying potassium current IK(ACh) in frog atrial myocytes. As suggested by previous studies, ACh inhibited the calcium current at concentrations (EC50 = 8 nM) significantly lower than those required for the activation of IK(ACh) (EC50 = 101 nM). The pharmacological profiles of the two responses suggest that despite the differences in agonist sensitivity, both are mediated by the same (m2) type of muscarinic receptors. Intracellular application of GDP beta S, an inhibitor of G protein function, completely abolished both responses, implying that both actions of ACh are coupled to effectors by G proteins. In contrast, intracellular application of pertussis toxin (PTX) shifted to higher concentrations (EC50 = 170 nM) but did not abolish inhibition of the calcium current by ACh even though the block of the IK(ACh) response was complete. Increasingly large PTX concentrations and/or prolonged PTX treatments revealed a limiting, PTX- resistant inhibitory component that appears to be mediated by a PTX- insensitive G protein distinct from that mediating IK(ACh). For the PTX- sensitive components, the different agonist dependencies of IK(ACh) activation and calcium current inhibition may imply that different G proteins mediate each response although alternate possibilities involving the same G protein either functionally sequestered and/or differentially affected by interactions with effectors, can not be ruled out. The Rockefeller University Press 1994-11-01 /pmc/articles/PMC2229240/ /pubmed/7876829 Text en 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
Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title_full Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title_fullStr Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title_full_unstemmed Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title_short Differential effects of pertussis toxin on the muscarinic regulation of Ca2+ and K+ currents in frog cardiac myocytes
title_sort differential effects of pertussis toxin on the muscarinic regulation of ca2+ and k+ currents in frog cardiac myocytes
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229240/
https://www.ncbi.nlm.nih.gov/pubmed/7876829