CARDIAC ELECTROPHYSIOLOGICAL EFFECTS OF U-50, 488H ON GUINEA-PIG PAPILLARY-MUSCLE

Intracellular microelectrodes were used to study the electrophysiologi cal effects of U-50,488H on guinea-pig papillary muscle. U-50,488H (10 (-5) M) caused a significant decrease in the maximum rate of depolariz ation and a decrease in the action potential duration. At high concent ration (5 x 10(-5) M) U-50,488H induced a significant decrease of rest ing potential, maximum rate of depolarization, action potential amplit ude and the action potential duration. The administration of MR-2266 ( 5 x 10(-7) M) partially antagonized the cardiac electrophysiological e ffects of U-50,488H. These results suggest that the electrophysiologic al effects of U-50,488H may be partially due to an interaction with op ioid receptors.