Potassium depletion increases proton pump ([H.sup.+]-ATPase) activity in intercalated cells of cortical collecting duct

Potassium depletion increases proton pump ([H.sup.+]-ATPase) activity in intercalated cells of cortical collecting duct. Am J Physiol Renal Physiol 279: F195-F202, 2000.--Intercalated cells (ICs) from kidney collecting ducts contain proton-transporting ATPases ([H.sup.+]-ATPases) whose plasma membrane expression is regulated under a variety of conditions. It has been shown that net proton secretion occurs in the distal nephron from chronically [K.sup.+]-depleted rats and that upregulation of tubular [H.sup.+]-ATPase is involved in this process. However, regulation of this protein at the level of individual cells has not so far been examined. In the present study, [H.sup.+]-ATPase activity was determined in individually identified ICs from control and chronically [K.sup.+]-depleted rats (9-14 days on a low-[K.sup.+] diet) by monitoring [K.sup.+]- and [Na.sup.+]-independent [H.sup.+] extrusion rates after an acute acid load. Split-open rat cortical collecting tubules were loaded with the intracellular pH ([pH.sub.i]) indicator 2',7'-bis (2-carboxyethyl)-5(6)-arboxyfluorescein, and [pH.sub.i] was determined by using ratiometric fluorescence imaging. The rate of [pH.sub.i] recovery in ICs in response to an acute acid load, a measure of plasma membrane [H.sup.+]-ATPase activity, was increased after [K.sup.+] depletion to almost three times that of controls. Furthermore, the lag time before the start of [pH.sub.i] recovery after the cells were maximally acidified fell from 93.5 [+ or -] 13.7 s in controls to 24.5 [+ or -] 2.1 s in [K.sup.+]-depleted rats. In all ICs tested, [Na.sup.+]- and [K.sup.+]-independent [pH.sub.i] recovery was abolished in the presence of bafilomycin (100 nM), an inhibitor of the [H.sup.+]-ATPase. Analysis of the cell-to-cell variability in the rate of [pH.sub.i] recovery reveals a change in the distribution of membrane-bound proton pumps in the IC population of cortical collecting duct from [K.sup.+]-depleted rats. Immunocytochemical analysis of collecting ducts from control and [K.sup.+]-depleted rats showed that [K.sup.+]-depletion increased the number of ICs with tight apical [H.sup.+]ATPase staining and decreased the number of cells with diffuse or basolateral [H.sup.+]-ATPase staining. Taken together, these data indicate that chronic [K.sup.+] depletion induces a marked increase in plasma membrane [H.sup.+]ATPase activity in individual ICs. proton-adenosinetriphosphatase; bafilomycin; intracellular pH; 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein; immunocytochemistry