Effect of CO₂ on intracellular pH in perfused bullfrog proximal tubules

Abstract

We investigated the effect of basolateral CO₂ on the cytosolic pH (pH_i) regulation in the proximal tubule of perfused bullfrog kidney by using H⁺-selective microelectrode. Furthermore, in sliced kidney, we monitored the changes in acridine orange fluorescence in acid vesicles of proximal tubule cells during the elevation of basolateral CO₂ with or without H⁺-pump inhibitors. Elevating baolateral CO₂ from 1.5 to 5% at constant HCO₃⁻ concentration induced an initial slight decrease followed by a sustained increase in pH_i with 10 mV hyperpolarization of basolateral membrane. In the presence of 10⁻⁶ M bafilomycin A1 (BAFA) or 10⁻⁷ M concanamycin A (CNCA), a specific H⁺-pump inhibitor, elevating basolateral CO₂ produced no increase in pH_i, but a decrease in pH_i with a depolarization of basolateral membrane. The increase in acridine orange intensity in acid vesicles was inhibited by the perfusion of 10⁻⁶ M BAFA during the elevation of CO₂ in the perfusion fluid. The peritubular perfusion of 10⁻⁶ M BAFA suppressed the alkalinaization of pH_i with 20 mM NH₃/NH₄⁺ application to peritubular perfusion fluid. These results indicate that intracellular H⁺ transport in the acid vesicles as well as Na⁺/H⁺ exchanger or Na⁺-HCO₃⁻ cotransporter in the cell membrane play an important role of the pH_i regulation in the proximal tubule of bullfrog kidney. [J Physiol Sci. 2006;56 Suppl:S140]