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The sodium-potassium ATPase (Na /K -ATPase or Na /K -pump) is an enzyme present at the surface of all eukaryotic cells, which actively extrudes Na from cells in exchange for K at a ratio of 3:2, respectively. Its activity also provides the driving force for secondary active transport of solutes such as amino acids, phosphate, vitamins and, in epithelial cells, glucose. The enzyme consists of two subunits ([alpha] and [beta]) each expressed in several isoforms. Many hormones regulate Na /K -ATPase activity and in this review we will focus on the effects of insulin. The possible mechanisms whereby insulin controls Na /K -ATPase activity are discussed. These are tissue- and isoform-specific, and include reversible covalent modification of catalytic subunits, activation by a rise in intracellular Na concentration, altered Na sensitivity and changes in subunit gene or protein expression. Given the recent escalation in knowledge of insulin-stimulated signal transduction systems, it is pertinent to ask which intracellular signalling pathways are utilized by insulin in controlling Na /K -ATPase activity. Evidence for and against a role for the phosphatidylinositol-3-kinase and mitogen activated protein kinase arms of the insulin-stimulated intracellular signalling networks is suggested. Finally, the clinical relevance of Na /K -ATPase control by insulin in diabetes and related disorders is addressed.

(C)1998 Kluwer Academic Publishers