Regulation of intracellular pH in avian renal proximal tubules

In proximal tubules isolated from chicken transitional nephrons, intracellular pH (pHi), measured with the pH-sensitive fluorescent dye 2'.7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF), was approximately 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 approximately 6.8 in response to NH4Cl pulse. The rate of recovery of pHi (dpHi/dt) from this acid level to the resting level and the resting pHi 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 dpHi/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+/Hi exchanger, a basolateral Na(+)-coupled Cl/HCO3 exchanger, a basolateral Na(+)-HCO3(-)CO(3)2 cotransporter, and a basolateral Na(+)-independent Cl-/HCO3 exchanger.