title: M2 and M3 muscarinic receptors couple, respectively, with activation of nonselective cationic channels and potassium channels in intestinal smooth muscle cells.
abstract: Smooth muscle cells of guinea pig ileum express both M2 and M3 subtypes of muscarinic receptors. Under voltage clamp, activation of the muscarinic receptors with carbachol (CCh) induces Ca2+-activated K+ current (I[K-Ca]) and nonselective cationic current (Icat). Receptor subtypes mediating the current responses were characterized by using pirenzepine, AF-DX116, 4-DAMP and atropine, which have different profiles of the affinity constants for muscarinic receptor subtypes. The muscarinic antagonists inhibited either CCh-evoked I(K-Ca) or Icat with different potencies. Their relative potencies for I(K-Ca) and Icat inhibition resembled the relative affinity constants for M3 and M2 subtypes, respectively. Thus, the I(K-Ca) is mediated via the M3 subtype and the Icat via the M2 subtype.
authors.affiliation: Department of Veterinary Science, Faculty of Agriculture, Gifu University, Yanagido, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Komori
authors.forename: T
authors.initials: T
authors.lastname: Unno
authors.forename: T
authors.initials: T
authors.lastname: Nakayama
authors.forename: H
authors.initials: H
authors.lastname: Ohashi
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D015221:Potassium Channels / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*
chemical_list: D018721:Muscarinic Agonists; D010880:Piperidines; D015221:Potassium Channels; D011976:Receptors, Muscarinic; D010890:Pirenzepine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D002217:Carbachol; C048593:otenzepad; D002118:Calcium