Specific inhibition of isoproterenol-stimulated cyclic AMP accumulation by M2 muscarinic receptors in rat intestinal smooth muscle.
The ability of oxotremorine-M to inhibit cyclic AMP accumulation in the presence of a variety of adenylate cyclase activators was studied in slices from the longitudinal muscle of the rat ileum. Oxotremorine-M was found to inhibit forskolin- and isoproterenol-stimulated cyclic AMP accumulation maximally by 17 and 32%, respectively, but not the stimulation due to other activators of adenylate cyclase. Inhibition of cyclic AMP accumulation by oxotremorine-M was unaffected by tetrodotoxin and was completely reversed by atropine. AF-DX 116 (11[[2-[(diethylamino)methyl]-1- piperidynyl]acetyl]-5,11-dihydro-6H-pyrido[2,3- b][1,4]benzodiazepine-6-one) an M2-selective antagonist, shifted the oxotremorine-M dose-response curve to the right with a dissociation constant (KB) of 0.20 microM, consistent with the dissociation constants for binding at the M2 muscarinic receptor site (KD = 0.092 microM) and inhibition of adenylate cyclase activity (KB = 0.13 microM). Hexahydrosiladifenidol, an M3-selective antagonist, shifted the oxotremorine-M dose-response curve to the right with a dissociation constant of 0.67 microM, again consistent with the dissociation constant for binding at the M2 site (KD = 0.83 microM). The agreement between the estimates of the dissociation constants of muscarinic antagonists for binding and for inhibition of cyclic AMP accumulation suggest that oxotremorine-M inhibition of isoproterenol-stimulated cyclic AMP accumulation in slices of rat intestinal smooth muscle is mediated by the M2 receptor.
Griffin
M T
MT
Department of Chemistry, Chapman University, Orange, California.
Ehlert
F J
FJ
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D005576:Colforsin / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D007545:Isoproterenol / Q000037:antagonists & inhibitors*; D008297:Male; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism; D010095:Oxotremorine / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism
D011976:Receptors, Muscarinic; D005576:Colforsin; D010095:Oxotremorine; C042743:oxotremorine M; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol