Creatine and the control of energy metabolism in cardiac and skeletal muscle cells in culture

The addition of creatine to the culture media in which either cardiac or skeletal muscle cells were grown resulted in an increased concentration of intracellular phosphorylcreatine. Since the only metabolic path known for the synthesis of phosphorylcreatine is via creatine phosphokinase, it is suggested that the mitochondrial enzyme activity was stimulated by creatine, and that the ADP formed as a product of the reaction became available for the oxidative phosphorylation. The rate of synthesis of ATP must have been stimulated prior to the net increase in phosphorylcreatine. This finding provides evidence that creatine might be involved in a regulatory feedback mechanism maintaining the energy source for contraction and not serving merely as an energy store in the muscle.