EFFECTS OF GLUCAGON, PROSTAGLANDIN E1 AND DIBUTYRYL CYCLIC 3', 5'-AMP UPON THE TRANSMEMBRANE ACTION POTENTIAL OF GUINEA PIG VENTRICULAR FIBER AND MYOCARDIAL CONTRACTILE FORCE

Effects of glucagon, prostaglandin El and dibutyryl cyclic 3', 5'-AMP upon the transmembrane action potential and the myocardial contractile force were investigated by using the isolated, perfused guinea pig heart by Langendorff's technique. The positive chronotropic and inotropic actions were observed by administering these agents into perfusion-cannula, and these effects were not blocked by propranolol. All of these agents produced shortening of the repolarization phase 2 (plateau phase) and increased the membrane resting potential in magnitude. The possible mechanisms underlying these changes is discussed in the light of cardiac cellular physiology and of the action of cyclic 3', 5'-AMP in the two messenger system.