Regulation of intracellular sodium concentrations in rat diaphragm muscle.

The concept is suggested that the sodium pump mechanism is influenced by the transmembrane electrical potential, and that the pump acts to maintain a constant electrochemical gradient for sodium. Evidence leading to this suggestion was obtained in rat diaphragm muscle by altering systematically the transmembrane chemical gradient for sodium ions and the transmembrane voltage. The voltage changes were produced by varying the extracellular and intracellular potassium ion concentrations. In each case the intracellular sodium concentration changed, presumably by activity of the sodium pump, so that the total electrochemical gradient for sodium was restored.