HORMONAL-REGULATION OF THE NA-K+-ATPASE - MECHANISMS UNDERLYING RAPIDAND SUSTAINED CHANGES IN PUMP ACTIVITY()

The sodium-potassium-activated adenosinetriphosphatase (Na+- K+-ATPase ; Na+-K+ pump) is a ubiquitous plasma membrane enzyme that catalyzes t he movement of K+ into cells in exchange for Na+. In addition, it prov ides the driving force for the transport of other solutes, notably ami no acids, sugar, and phosphate. The regulation of Na+-K+ ATPase in var ious tissues is under the control of a number of circulating hormones that impart both short- and long-term control over its activity. The m olecular mechanisms by which hormones alter Na+-K+-ATPase activity hav e only begun to be studied. In this review, we assess the acute and lo ng-term actions of a number of hormones (aldosterone, thyroid hormone, catecholamines, insulin, carbachol) on the Na+-K+ pump. The long-term regulation exerted by thyroid hormone and aldosterone is mediated by changes in gene expression. The short-term regulation exerted by catec holamines is mediated by reversible phosphorylation of the pump cataly tic subunit. Recent evidence supports regulation of the pump by phosph orylation in vitro and in intact cells. Finally, in some tissues the r apid action of insulin, aldosterone, and carbachol involves changes in the subcellular distribution of pump units.