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

P. Michal, E. E. El-Fakahany, V. Doležal

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46 Scopus citations


Muscarinic M2 receptors preferentially couple with the G i/o class of G-proteins to inhibit cAMP synthesis. However, they can also stimulate net synthesis of cAMP and inositol phosphate (IP) accumulation. We investigated in intact Chinese hamster ovary (CHO) 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 Gsα 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 an EC50 of 79 μM. Removal of the Gq, G11, or both α subunits reduced this response by 78, 54, and 92%, respectively, whereas suppression of the Gsα subunit had no effect. Similar results obtained in CHO cells expressing M1 receptors that preferentially couple with G s and Gq/11 G-proteins confirmed the 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 [N,N,N-trimethyl-4-(2-oxo-1- pyrolidinyl)-2-butyn-1-ammonium] behaved as full agonists, furmethide (N,N,N-trimethyl-2-furanmethammonium) and methylfurmethide [(5-methyl-2-furyl) methyltrimethylammonium] were partial agonists, and oxotremorine (1-[4-(1-pyrrolidinyl)-2-butynyl]-2-pyrrolidinone) had no effect. Our results provide direct evidence of M2 receptor coupling with the α 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 the agonist used.

Original languageEnglish (US)
Pages (from-to)607-614
Number of pages8
JournalJournal of Pharmacology and Experimental Therapeutics
Issue number2
StatePublished - Feb 2007


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