Adaptation of inner medullary collecting duct vacuolar H-adenosine triphosphatase to chronic acid or alkali loads in the rat.

Acidosis increases and alkalosis decreases proton secretion in the inner medullary collecting duct (IMCD). We examined the mechanism of this adaptation by studying the immunocytochemical distribution of the vacuolar H-adenosine triphosphatase (ATPase) in the IMCD from rats subjected to acid or alkali loads for a mean duration of 4 and 9 days. For immunocytochemical staining, a monoclonal antibody to the 31-kD subunit of the bovine kidney vacuolar H-ATPase was used. Intercalated cells were present only in the initial IMCD, and the principal cells and IMCD cells showed no appreciable H-ATPase staining under any experimental conditions. We found significant adaptive changes in the distribution of H-ATPase in the intercalated cells of the IMCD. H-ATPase staining in acid-loaded rats shifted from cytoplasmic vesicles to apical plasma membrane, whereas in alkali-loaded rats cytoplasmic vesicular staining was enhanced and staining of plasma membrane disappeared. These adaptive changes were most prominent on day 4 of acid-loaded and days 4 and 9 of alkali-loaded rats. Our results indicate that translocation of the H-ATPase pump between cytoplasmic vesicles and apical plasma membrane of the intercalated cells is an important mechanism is adaptation of the IMCD to chronic acid base perturbations.