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 similar to 7.3-7.4 under control conditions [N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium with pH 7.4 at 39 degrees C] and was reduced to similar 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 bath 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 pH(i) and the rate of recovery of pH(i) 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-, CO32- cotransporter, and a basolateral Na+-independent Cl-/HCO3- exchanger.