title: Characterization of M2 muscarinic receptor activation of different G protein subtypes.
abstract: The M2 muscarinic acetylcholine receptor (mAChR) expressed in insect cells (Spodoptera frugiperda, Sf9) using the baculovirus system formed active functional complexes with coexpressed Gi as well as with Go proteins, while no complexes could be detected with internal G proteins. Comparison of the abilities of different muscarinic agonists and partial agonists to increase [35S]GTPgammaS binding revealed no significant differences between M2/Gi and M2/Go complexes neither with respect to affinities nor efficacies of the ligands studied. Coexpression with either G protein caused constitutive activity of the receptor amounting up to 66% of stimulable [35S]GTPgammaS binding. Muscarinic antagonists, like atropine, scopolamine and N-methylscopolamine, behaved as inverse antagonists with potencies in good agreement with their binding affinities to the receptor. The results implicate that the functional reconstitution of M2 muscarinic receptor with either Gi or Go proteins in insect cells provides a valuable tool for screening of potencies as well as efficacies of agonists, partial agonists and inverse agonists at this receptor.
authors.affiliation: Institute of Organic and Bioorganic Chemistry, University of Tartu, Jakobi Str. 2, EE-51014 Tartu, Estonia.
authors.forename: Ain
authors.initials: A
authors.lastname: Uustare
authors.forename: Johnny
authors.initials: J
authors.lastname: Näsman
authors.forename: Karl E O
authors.initials: KE
authors.lastname: Akerman
authors.forename: Ago
authors.initials: A
authors.lastname: Rinken
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D007313:Insecta; D008024:Ligands; D018721:Muscarinic Agonists / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D011869:Radioligand Assay; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic / Q000187:drug effects*
chemical_list: D006150:Guanine Nucleotides; D008024:Ligands; D018721:Muscarinic Agonists; D043585:Receptor, Muscarinic M2; D011976:Receptors, Muscarinic; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D019204:GTP-Binding Proteins