Na-K pump: Multiple isoforms and their roles in cardiac functions

Abstract

The primary role of the Na-K pump is the generation and maintenance of transmembrane Na+ and K+ gradients. The Na-K pump actively transports these ions across the cell membrane against concentration gradients. Although there are other mechanisms and ion channels that modify intracellular Na+ and K+ concentrations, the Na-K pump is essential for maintaining an intracellular environment of low Na+ and high K+ concentrations. The K+ and Na+ gradients in turn are the basis for transmembrane potentials, membrane excitability, and action potentials in the cardiac muscle. In addition, activity of the Na-K pump indirectly modulate intracellular Ca2+ concentrations through the Na/Ca exchanger. A low intracellular Ca2+ concentration is necessary for relaxation of heart muscle, proper functions of mitochondria, and Na-K pump activity. Equally important is the function of Na+, K+-ATPase as the only known receptor for cardiac glycosides.