ACTIVATION OF ACID-SECRETING INTERCALATED CELLS IN RABBIT COLLECTING DUCT WITH AMMONIUM-CHLORIDE LOADING

In normal rabbit, immunolabeling of intercalated cells in the outer me dullary collecting duct (OMCD) demonstrates band 3-like protein in the basolateral plasma membrane (15) and H+-adenosinetriphosphatase (H+-A TPase) in the apical plasma membrane and cytoplasmic vesicles (30). Ho wever, in type A intercalated cells in the cortical collecting duct (C CD), band 3-like protein is located primarily in multivesicular bodies and cytoplasmic vesicles (15), whereas H+-ATPase is present in cytopl asmic vesicles only in most intercalated cells (30). In this study, we observed the effect of chronic acid loading on immunolocalization of these transporters in the collecting duct. Adult New Zealand White rab bits received either normal tap water (controls) or 75 mM NH4Cl for 12 days plus eight daily gavages of 2-6 meg NH4Cl/kg body wt. At time of death, mean urine pH of acid-loaded animals was 5.96 (SD = 0.69), vs. 8.47 (SD = 0.07) in controls. Kidneys were fixed by in vivo perfusion and processed for light and electron microscopic immunoperoxidase loc alization of band 3-like protein and immunogold localization of H+-ATP ase. In controls, band 3-like protein was largely confined to multives icular bodies in the majority of positive-staining intercalated cells in the CCD and to the basolateral plasma membrane of intercalated cell s in the OMCD. In acid-loaded rabbits, band 3 protein-positive interca lated cells in the inner CCD and the in the outer stripe of the OMCD ( OMCD(0)) were strikingly stellate in form. Basolateral plasma membrane label was intensified, while the number of labeled multivesicular bod ies was diminished. Morphometric analysis demonstrated an increase in the amount of basolateral plasma membrane in these intercalated cells. In control rabbits, H+-ATPase immunoreactivity in intercalated cells in the CCD was located predominantly over cytoplasmic vesicles. A mino rity of intercalated cells exhibited basolateral plasma membrane label , and only an occasional cell displayed apical plasma membrane label. In acid-loaded rabbits, H+-ATPase immunoreactivity was enhanced along the apical plasma membrane of intercalated cells in the inner CCD, and morphemetric analysis demonstrated increased apical plasma membrane i n band 3-positive intercalated cells in this segment. These results su ggest that rabbits respond to acid loading via enhancement of both ele ctrogenic proton secretion and Cl-/HCO3- exchange in intercalated cell s in the inner CCD and the OMCD(0).