Regulation of intracellular pH in avian renal proximal tubules

In proximal tubules isolated from chicken transitional nephrons, intracellular pH (pH(i)), measured with the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5,6 carboxyfluorescein (BCECF), was -7.3-7.4 under control conditions [N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid- buffered medium with pH 7.4 at 39°C] and was reduced to ~6.8 in response to NH₄Cl pulse. The rate of recovery of pH(i) (dpH(i)/dt) from this acid level to the resting level and the resting pH(i) were 1) significantly reduced by the removal of Na⁺ from the bath, 2) significantly increased by the removal of Cl^- from the bath, and 3) unchanged by the removal of both Na⁺ and Cl^- from the bath. The addition of either amiloride or 4,4'- diisothiocyanostilbene-2,2'-disulfonate to the both reduced dpH(i)/dt to about the same extent as the removal of Na⁺. These data suggest that both Na⁺-coupled and Cl^--coupled acid-base fluxes at the basolateral membrane are involved in determining the resting phi and the rate of recovery of phi after acidification. The most likely possibilities appear to be a basolateral Na⁺/H⁺ exchanger, a basolateral Na⁺-coupled Cl^-/HCO₃ exchanger, a basolateral Na⁺-HCO₃-CO₃/²⁺ cotransporter, and a basolateral Na⁺- independent Cl^-/HCO₃ exchanger.