[Effect of a sodium transmembrane gradient on efflux of creatinine from the myocardium]

Heart maintains a gradient for creatine under physiological conditions, so that creatine release is relatively small. Calcium depletion, addition of strophanthin or decrease of sodium concentration (till 80 mM) provoke release of creatine. Elevation of transmembrane sodium gradient by raising of extracellular sodium concentration prevented loss of creatine. The effect of elevated concentration of sodium ions was blocked by strophanthin but depended on osmolarity, because solutions with the same osmolarity that hypersodium media had no protective effect on release of creatine. A sarcolemmal mechanism of Na creatine cotransports is proposed.