sodium-potassium (Na-K) pump

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sodium-potassium (Na-K) pump

one of many similar molecular complexes embodying ion-binding sites and an ATPase, found in surface (plasma) membrane of all cells, which actively transports sodium ions (Na+) out of the cytoplasm and potassium ions (K+) into it (usually in the ratio 3Na+ out to 2K+ in), using energy derived from hydrolysis of ATP by the action of sodium-potassium (Na-K) ATPase . All cells have at least a minimum density of these pumps but nerve and muscle cells have greater numbers to cope with the greater ion fluxes in these cells. The high intracellular [K+] and low intracellular [Na+] in cells (in contrast to their concentrations in extracellular fluid) are due to these pumps; the maintenance of the membrane potential and of cell volume results from this ion distribution. Formerly, on the basis of inadequate understanding, termed simply 'sodium pump'. See also cell.
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