Regulation of principal cell pH by Na/H exchange in rabbit cortical collecting tubule

Summary Changes in intracellular pH (pH_i) were measured using the pH indicator, BCECF, in principal cells from split opened cortical collecting tubules (CCTs) derived from rabbits maintained on a normal diet. This monolayer preparation has the advantage of allowing us to visualize the morphological differences in the two major cell types in this nephron segment under transmitted light. The visual identification of the cell types was verified using emission measurements taken from single principal and intercalated cells in the opened tubule which had been exposed to fluorescein isothiocyanate (FITC)-labeled peanut lectin. We confirmed the existence of an amiloride-sensitive Na/H exchange process activated during intracellular acidosis in principal cells. In addition, the exchanger was active under basal conditions and over a wide range of pH_i. Because the exchanger was active under basal conditions we tested the hypothesis that changes in intracellular Na (Na_i) would alter pH_i in a predictable way. Maneuvers designed to alter Na_i were without significant effects within a 10-min time frame. Specifically, addition of 100 m ouabain to increase Na_i or exposure of the tubules to 10^–5m amiloride to decrease luminal Na entry and reduce Na_i did not have an effect on pH_i. In some experiments we did observe however, after a 30-min exposure to ouabain, a small decrease in pH_i. These results suggest that Na/H exchange is a major regulator of pH_i in principal cells. However, regulation of Na transport by changes in pH_i in principal cells of rabbit CCT via the activity of a Na/H exchanger do not seem to contribute to the feedback control of Na transport.This work was supported by U.S. Public Health Service grants DK27847 to L.G. Palmer and DK11489 to E.E. Windhager.