[Relationship between the strength of myocardial fiber contraction of frog heart ventricle and processes of intracellular energy transport].

At 10--15 mM of creatine in the perfusate the force of the myocardium contraction was increased. At concentrations over 40 mM, creatine causes a decrease of contractile force which can be significantly increased after washing-out of the excess of creatine. Prolonged perfusion (over 10 hrs) with Ringer's solution leads to a decrease in intracellular creatine concentration and to a parallel decrease of contractile force. Under these conditions the intracellular concentration of creatine phosphate is significantly decreased with small changes in ATP content. The addition of creatine to perfusate leads to the complete restoration of contractile force and creatine phosphate content in heart strips' cells. These results indicate that the contractile force of heart strips depends upon high energy phosphate content (mainly creatine-phosphate content) in the cells and are consistent with the idea of the existence of the creatinephosphate pathway of energy transport in heart cells.