Stimulation of cyclic AMP-dependent protein kinase in rat atria by (-)-CGP 12177 through an atypical beta-adrenoceptor

Mammalian hearts possess an atypical beta-adrenoceptor (non-beta(1), non-beta(2), non-beta(3)) through which (-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one ((-)-CGP 12177) causes cardiostimulant effects. Here we showed that (-)-CGP 12177 increased the activity of adenosine 3':5'-cyclic monophosphate (cyclic AMP)-dependent protein kinase in the presence of 200 nM (-)-propranolol in rat atria at a concentration (10 mu M) that elicits maximum positive chronotropic and inotropic effects. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) potentiated the positive chronotropic and inotropic effects of (-)-CGP 12177. We suggest that the atypical beta-adrenoceptor is coupled positively to the Gs protein-adenylyl cyclase system.