DISTAL NEPHRON ANION TRANSPORT

Acid-base and chloride balance are maintained primarily by the kidney; final regulation of urinary acid-base and chloride composition is achieved by the collecting duct system. Bicarbonate and chloride transport by the collecting tubule appear to be regulated by Beta-adrenergic agents and chronically in response to systemic acid-base disturbances. The present proposal addresses the mechanisms of acute and chronic regulation of anion transport using isolated, perfused tubules and cultured collecting tubule cells. The methods used include ion fluxes, electrophysiologic measurements, and immunocytochemistry. The first specific aim is to examine several possible mechanisms by which cyclic AMP stimulates HCO3 reabsorption in both perfused tubules and cultured cells. The hypotheses examined include insertion of H+-pumps into the apical cell membrane, increasing a basolateral membrane C1 conductance, or regulating the insertion of a C1-HCO3 exchange protein into the basolateral membrane. The second specific aim looks at the mechanisms by which in vivo acid-base disturbances chronically regulate anion transport in intact collecting tubule cells. The approach is a combination of functional flux measurements on perfused tubules and both light and electron microscopical quantitation of various anion transport cell types. The two opposing hypotheses being tested are that reversal of net bicarbonate transport either occurs by differential stimulation/suppression of two different vectorally-fixed cell types or it occurs via reversal of the anion transporting components of individual collecting tubule cells. The third aim is to functionally and cytochemically characterize anion-transporting cells in tissue culture. The last aim is to use these cultured anion-transporting cells to study the mechanisms by which systemic acid-base disturbances such as metabolic and respiratory acidosis and alkalosis cause chronic regulation of collecting duct anion transport. The results in cultured cells will be compared to preceding results in intact tubules. These studies will be directly important for our understanding of such disease states as renal tubular acidosis and metabolic alkalosis, as well as for an understanding of renal compensatory mechanisms in respiratory acidosis and alkalosis.