[Renal K-ATPases: structure, function and dysfunction]

Na,K-ATPase and H,K-ATPase consist of two transmembrane proteins, the larger of which (catalytic subunit) exchanges extracellular K+ against intracellular Na+ or proton, at the expense of ATP hydrolysis. Cloning of four isoforms of Na,K-ATPase and two isoforms of H,K-ATPase has provided a molecular basis to the functional heterogeneity of these ATPases. Besides its house keeping functions, renal Na,K-ATPase energizes most solute and water transports along the whole nephron. For this purpose, it utilizes about 80% of renal metabolic energy. H,K-ATPase, which is restricted to the renal collecting duct, has a more limited role: it energizes K+ reabsorption during hypokalemia and, along with H-ATPase, participates to acid/base homeostasis. Dysregulation of tubular Na,K-ATPase and H,K-ATPase are involved in physiopathological alterations. For examples, results are presented which show the relationships that exist between a) Na+ retention during experimental nephrotic syndrome and stimulation of collecting duct Na,K-ATPase, and b) kaliuretic effect of loop diuretics and inhibition of collecting duct H,K-ATPase.