Agonists differentiate muscarinic receptors that inhibit cyclic AMP formation from those that stimulate phosphoinositide metabolism.

摘要: Muscarinic receptor stimulation elicits two distinct biochemical responses in embryonic chick heart cells: inhibition of catecholamine-stimulated cyclic AMP formation and phosphoinositide (PhI) hydrolysis. We observe major differences the effects agonists on these responses. First, carbachol oxotremorine both inhibit formation, but only stimulates PhI Second, dose-response relationships for differ; half-maximal concentrations needed to cAMP accumulation stimulate hydrolysis are 2 X 10(-7) 10(-5) M, respectively. carried out radioligand binding studies intact cells determine whether data could be explained terms different agonist states muscarinic receptor. In cells, competes [3H]quinuclidinyl benzilate-binding sites with high low affinity, while shows affinity binding. suggest that state common is associated adenylate cyclase, very site seen response. also consider possibility caused by a single efficiently coupled cyclase inefficiently Whichever mechanism correct, our findings demonstrate receptors response can differentiated virtue their sensitivity efficiency which some induce change elicit receptor-mediated