Basolateral regulation of pH(i) in proximal tubules of avian loopless and long-looped nephrons in bicarbonate

In isolated, nonperfused chicken proximal tubules from both loopless reptil ian-type and long-looped mammalian-type nephrons, resting intracellular pH (pH(i)), measured with pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethy l)-5,6-carboxyfluorescein (BCECF), was similar to 7.1 under control HCO3- c onditions [20 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES )/5 mM HCO3--buffered medium with pH 7.4 at 37 degrees C] and was reduced t o similar to 6.8 in response to NH4Cl pulse. The rate of recovery of pH(i) (dpH(i)/dt) from this level to the resting level in proximal tubules from b oth nephron types was (1) significantly reduced by the removal of Na+ or bo th Na+ and Cl- from the bath, and (2) unaffected by the removal of Cl- from the bath or the presence of a high K+ concentration or Ba2+ in the bath. I n proximal tubules from long-looped mammalian-type, but not loopless reptil ian-type, nephrons, dpH(i)/dt was significantly reduced by the addition of either 5-(N-ethyl-N-isopropyl) amiloride (EIPA) or 4,4'-diisothiocyanostilb ene-2,2'disulfonate (DIDS) to the bath. These data suggest that a Na+/H+ ex changer and most likely a Na+-dependent Cl-/HCO3- exchanger are involved in basolateral regulation of pH(i) in mammalian-type nephrons whereas none of the commonly identified basolateral acid-base transporters appear to be in volved in regulation of pH(i) in reptilian-type nephrons. J. Exp. Zool. 284 :174-187, 1999. (C) 1999 Wiley-Liss, Inc.