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(or sodium-potassium pump), in biochemistry, a membrane mechanism that maintains a definite ratio of Na + and K + ions in cells by active transport of the ions against electrochemical and concentration gradients. The cells of most tissues contain more K + ions than Na + ions, whereas the fluids reaching the tissues (blood, lymph, and intercellular fluid) contain significantly higher concentrations of Na +. A certain number of ions continuously enters and leaves the cells. The passive transport of cations (transfer of ions through the membrane by means of a system of special channels along the electrochemical and concentration gradients) is, on the average, compensated by active ion transport.
The function of the sodium pump is related to the transfer of metabolites into the cells and, in the case of nerve and muscle fibers, is also related to the mechanism of excitation. The active transfer of Na + from the cell is associated with the transport of K + in the opposite direction and is accomplished by a special enzyme system, the sodium-potassium transport system, which is stimulated by adenosine triphosphatase localized in the cell membrane. By hydrolyzing adenosine triphosphate (ATP), adenosine triphosphatase liberates energy, which is expended on the active transfer of cations. The working of the sodium pump on the whole depends on the level of cell metabolism.
R. N. GLEBOV