Response of the collecting duct to disturbances of acid-base and potassium balance.

With light microscopy and scanning electron microscopy, the epithelium of the collecting duct was examined in rats with acute and chronic acid-base disturbances, hypokalemia, hyperkalemia, and during osmotic diuresis and hydropenia. Acid-base disturbances included acute respiratory acidosis, acute metabolic alkalosis, and chronic metabolic acidosis. Two groups of hypokalemic animals were studied, those with and those without an associated metabolic alkalosis. After the appropriate physiologic data were collected, all kidneys were preserved for morpholigic data were collected, all kidneys were preserved for morphologic evaluation by in vivo intravascular perfusion fixation. The percentage of intercalated cells in the epithelium of the collecting duct in the cortex and outer medulla of each kidney was determined by light microscopic examination of 1-mu-thick Epon sections stained with toluidine blue. Qualitative observations were performed with scanning electron microscopy. Intercalated cells represented 36 to 40% of the epithelial cells forming the collecting duct in the cortex and outer and inner stripes of the outer medulla in control animals during hydropenia and during mild osmotic diuresis. No experimental condition studied was found to influence significantly the actual or relative number of intercalated cells, or their distribution in the collecting duct. The hypertrophy of both principal cells and intercalated cells in potassium-depleted animals occurred in both the presence and the absence of metablic alkalosis. Conclusion. Under the conditions of this study, intercalated cells represent a constant population of epithelial cells in the rat collecting duct, and intercalated and principal cells represent distinct cell typs, each defined by rather constant morphologic features. Contrary to previous reports, no evidence was found that a disturbance of hydrogen ion and potassium balance is associated with a conversion of principal to intercalated cells in the collecting duct.