ELECTROPHYSIOLOGICAL EFFECTS OF OPIOID RECEPTOR-SELECTIVE AGONISTS ONGUINEA-PIG PAPILLARY-MUSCLE

The cardiac electrophysiological effects of DAMGO, DPDPE and U-50,488H which are selective opioid agonists for mu, delta and kappa receptors , respectively, were studied in the isolated guinea-pig right ventricu lar papillary muscles. Neither DAMGO (5.10(-6)-5.10(-5)M) nor DPDPE (5 .10(-6)-5.10(-5)M) produced any significant effect on the action poten tial characteristics. However, U-50,488H (10(-5), 5.10(-5) M) caused a concentration-dependent reduction in the maximum rate of depolarizati on of phase 0 (V-max) and in the action potential duration measured at 50% repolarization, APD(50) and 90% repolarization, APD(90). At 5.10( -5) M it also produced a decrease of action potential amplitude (APA). These results suggest that the reported electrophysiological effects of U-50,488H on the cardiac muscle action potential, may be, at least in part, explained by a direct cardiac action.