sodium pump A mechanism by which sodium ions are transported out of a eukaryotic cell across the plasma membrane. The process requires energy in the form of ATP, being a form of active transport. The most important type is sodium/potassium ATPase (Na⁺/K⁺ ATPase), which is a membrane transport protein that exchanges sodium ions (Na⁺) for potassium ions (K⁺), thus maintaining the differential concentrations of each ion across the plasma membrane. This differential is vital to cellular function, e.g. in establishing the resting potential of a neuron.

sodium pump A mechanism found in higher animal cells that is responsible for the active transport of sodium and potassium ions across membranes and against concentration gradients. Its operation is dependent upon the provision of cellular ATP and the enzyme sodium/potassium-ATPase, and its net results are low levels of sodium ions and high levels of potassium ions inside the cell (compared with those outside). See also COUNTER-CURRENT EXCHANGE.