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[Role of creatine phosphokinase systems in regulating the force of myocardial contraction in frog ventricles].

Creatine phosphate (10 and 20 mM) increased both the force of contraction and action potential duration in isolated frog heart strips. In concentration of 75 mM creatine phosphate increased the force of contraction during first minutes with its following decrease. Action potential duration was also increased during this period. These data suggest existence of receptory sites for creatine phosphate in the heart cells: the myofibrillar creatine phosphokinase system where creatine phosphate increases the force of contraction; and the cellular membranes where creatine phosphate decreases the rate of membrane repolarization. Dinitrofluorobenzene (1.5 mM) completely inhibited contraction of the heart strips and significantly decreased the duration and intensity of action potential. The data obtained are discussed from the view--point of existence of a creatine phosphate pathway for intracellular energy transport in the heart cells.