SODIUM PUMP

in cellular physiology, a mechanism that has been identified in many cells and probably occurs in all and that maintains the internal concentration of potassium ions higher than that in the surrounding medium (blood, body fluid, water) and maintains the internal concentration of sodium ions very much lower than that of the surrounding medium. The pump has been identified with an enzyme, an adenosine-triphosphatase (ATPase), bound to the cell membrane and activated by external and internal . This enzyme uses metabolic energy to transport (pump) Na+ outward and K+ inward. Such pumps do not generally alter the distribution of electric charge across the membrane and hence do not produce a current (i.e., are not electrogenic). The resting potential of cells and related bioelectric phenomena such as the action potential depend on the steady state difference in concentrations of Na+ and K+ maintained by the pump. Other ion pumps, transporting different ions, are known for the cells of plant roots, vertebrate stomach, and vertebrate muscle.