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Journal of Pharmacology And Experimental Therapeutics Fast Forward
First published on October 25, 2006; DOI: 10.1124/jpet.106.114314

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Received for publication September 19, 2006.
Revised October 23, 2006.
Accepted for publication October 24, 2006.

Muscarinic M2 receptors directly activate Gq/11 and Gs G-proteins

Pavel Michal 1, Esam E El Fakahany 2, Vladimir Dolezal 1*

1 Institute of Physiology CAS 2 University of Minnesota Medical School

* Address correspondence to: E-mail: dolezal{at}biomed.cas.cz

Abstract

Muscarinic M2 receptors preferentially couple with the Gi/o class of G-proteins to inhibit cAMP synthesis. However, they can also stimulate net synthesis of cAMP and inositolphosphates (IP) accumulation. We investigated in intact Chinese hamster ovary cells expressing human M2 receptors (CHO-M2 cells) whether direct interaction of M2 receptors with Gs and Gq/11 G-proteins is responsible for the latter effects. Suppression of the Gs{alpha} subunit using RNA interference abolished stimulation of cAMP synthesis induced by 1 mM carbachol in both control and pertussis toxin-treated CHO-M2 cells but had no effect on the inhibition of forskolin-stimulated cAMP synthesis. Carbachol stimulated accumulation of IP with EC50 of 79 µM. Removal of the Gq, G11, or both {alpha} subunits reduced this response by 78%, 54%, and 92%, respectively, while suppression of the Gs {alpha} subunit had no effect. Similar results obtained in CHO cells expressing M1 receptors that preferentially couple with Gs and Gq/11 G-proteins confirmed efficiency of siRNA treatments. Stimulation of M2 receptors in control and pertussis toxin-treated cells by a series of full agonists with respect to inhibition of adenylyl cyclase displayed different efficacies in stimulating IP accumulation. Carbachol, acetylcholine and oxotremorine-M behaved as full agonists, furmethide and methylfurmethide were partial agonists, and oxotremorine had no effect. Our results provide direct evidence of M2 receptor coupling with the {alpha} subunits of Gs and Gq/11 G-proteins and demonstrate induction of multiple receptor conformational states dependent on both the concentration and the nature of used agonist.


Key words: G-protein, RNA interference, cAMP, inositolphosphates, muscarinic receptors, receptor-G-potein coupling


This article has been cited by other articles:


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M. T. Griffin, K. W. Figueroa, S. Liller, and F. J. Ehlert
Estimation of Agonist Activity at G Protein-Coupled Receptors: Analysis of M2 Muscarinic Receptor Signaling through Gi/o,Gs, and G15
J. Pharmacol. Exp. Ther., June 1, 2007; 321(3): 1193 - 1207.
[Abstract] [Full Text] [PDF]


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