Characterization and regulation of H-K ATPase in intercalated cells of rabbit cortical collecting duct

K-dependent H⁺ extrusion was investigated using fluorescence techniques in rabbit cortical collecting tubules (CCTs). Experiments were performed in split-open tubules from normal animals exposed to the intracellular pH indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). This preparation permitted the study of individual intercalated cells (Ics). In the Ics, partial recovery of pH<INF>i</INF> was observed in response to an acute acid load upon readdition of 5 mM K to the superfusate. This recovery was SCH 28080-inhibitable (10^–5 M) and ouabain-insensitive suggesting the process is mediated by a gastric-type H-K ATPase. To see if H-K ATPase plays a role in acid secretion its function was evaluated under chronic metabolic acidosis (CMA) conditions. CMA was induced by replacing drinking water with 75 mM NH<INF>4</INF>Cl in 5% sucrose for 10–14 days. The SCH 28080-inhibitable K-dependent pH<INF>i</INF> recovery rate was three-fold higher in CMA ICs compared to controls. To determine the location of the H-K ATPase, CCTs were microperfused and individual peanut lectin binding (PNA) ICs studied. K-dependent pH<INF>i</INF> recovery was measured in response to an NH<INF>4</INF>Cl pulse. An apical SCH 28080-inhibited K-dependent pH<INF>i</INF> recovery process was observed in control and CMA Ics. Taken together these data confirm the existence of a gastric-type H-K ATPase in ICs of rabbit CCT. Based on our findings the H-K ATPase is found on the apical side of the cell and is stimulated under conditions of CMA. J. Exp. Zool. 279:443–455, 1997. © 1997 Wiley-Liss, Inc.