Relationship between Cellular Calcium and Catecholamine on Myocardial Contractility

Abstract

Positive inotropic action of norepinephrine were demonstrated in rabbit heart that was perfused by solution containing various calcium concentration. In these experiments, the changes of calcium content in subcellular fractions of myocardium were observed. 1) The calcium concentration in each subcellular fraction of myocardium was increased in the state of increasing contractile force by norepinephrine. Especially, there are similar pattern of changes between calcium concentration in heavy microsome fraction and contractile force of myocardium. 2) Increase of cardiac rate had no effects on the changes of calcium concentration in myocardium. These phenomena induced by norepinephrine were inhibited by pretreatment of propranolol. Thus, it should be emphasized that calcium ion in cardiac sarcoplasmic reticulum plays an important role in increasing contractile force by norepinephrine.