Mode of Action of Catecholamines on Contraction Mechanism in Relation to Action Potential

Abstract

1) Catecholamines induced shortening of plateau and total duration of action potential and increase of contraction and shortening of the time to peak tension and of the total duration of contraction of the rabbit ventricular muscle. Some parallelism was found between the electrical and mechanical changes. 2) The findings suggest the following: isoproterenol utilizes chiefly the extracellular calcium for its inotropic action. Norepinephrine shows an inotropic action by mobilizing in addition the intracellular calcium, and the contraction by this action is depressed by potassium. Both have little relation with sodium in their inotropic action.