TIME COURSE OF SODIUM-INDUCED NA+-K+-ATPASE RECRUITMENT IN RABBIT CORTICAL COLLECTING TUBULE

In cortical collecting tubules (CCD) of aldosterone-repleted rabbit kidney, an increase in intracellular sodium concentration (Na(i)) induces the recruitment and/or activation of latent Na+-K+-ATPase pumps (Blot-Chabaud et al., J. Biol. Chem. 265: 11676-11681, 1990). The present study was addressed to determine the time course of this Na(i)-dependent pump recruitment and to examine some of the factors possibly involved in this phenomenon. CCD from adrenalectomized rabbits complemented with aldosterone and dexamethasone were incubated at 4-degrees-C either in a K+-free saline solution (Na+-loaded CCD) or in a sucrose solution (control CCD) and then rewarmed for various time periods to allow pump recruitment to occur. The number of pumps in the membrane was determined by specific [H-3]ouabain binding; Na(i) was measured using Na-22. A rise in Na(i) induced a threefold increase in the number of basolateral pumps, which was fully achieved within 1-2 min. This pump recruitment was reversible within 15 min after restoration of low Na(i). It was unaffected by inhibitors of cytoskeleton and Ca2+ ionophore A 23187. The blocker of the Na+-H+ antiporter, amiloride, did not prevent it. The protein kinase C activator, phorbol 12-myristate 13-acetate, did not induce it in the absence of Na+. We conclude that Na(i) is a major determinant of pump recruitment and/or activation, which occurs over a very short period of time. It may constitute a rapid adaptative response to an increase in the cell Na+ load.