Uncoupling the Sodium Pump

Abstract

IT is now widely accepted that the extrusion of sodium from living cells is associated with the splitting of ATP at the inside surface of the cell membrane^1–7. The mechanism responsible is inhibited by cardiac glycosides and it is affected in a complicated way by potassium ions. With membrane preparations from most cells, glycoside-sensitive ATPase activity can be demonstrated only when both sodium and potassium are present⁵, and in red cells and nerve there is evidence that the sodium ions must be inside and the potassium ions outside^6,7. This fits in with the known coupling between sodium efflux and potassium influx in these tissues, and suggests that under normal conditions the transport mechanism catalyses an exchange of sodium ions for potassium ions across the membrane using energy from the hydrolysis of ATP at the internal surface.