The cell-surface Na⁺/K⁺-ATPase is an integral membrane protein which regulates the membrane potential of the cell by maintaining gradients of Na⁺ and K⁺ ions across the plasma membrane, also making a small, direct contribution to membrane potential, particularly in cardiac cells. For every molecule of ATP hydrolysed, the Na⁺/K⁺-ATPase extrudes three Na⁺ ions and imports two K⁺ ions. The active transporter is a heteromultimer with incompletely defined stoichiometry, possibly as tetramers of heterodimers, each consisting of one of four large, ten TM domain catalytic α subunits and one of three smaller, single TM domain glycoprotein β-subunits (see table). Additional protein partners known as FXYD proteins (e.g. FXYD2, P54710) appear to associate with and regulate the activity of the pump.

Na⁺/K⁺-ATPases are inhibited by ouabain, and cardiac glycosides such as digoxin, as well as potentially endogenous cardiotonic steroids [1].

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