Regulation of intracellular pH in proximal tubules of avian long-looped mammalian-type nephrons

In nonperfused proximal tubules isolated from chicken long-looped mammalian-type nephrons, intracellular pH (pH(i)), measured with the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, was similar to 7.3 under control conditions (HEPES-buffered medium with pH 7.4 at 37 degrees C) and was reduced to similar to 7.0 in response to NH4Cl pulse. The rate of recovery of pH(i) from this level to the resting level was 1) significantly reduced by the removal of Na+ from the bath, 2) significantly increased by the removal of Cl- from the bath, 3) unchanged by the removal of both Na+ and Cl- from the bath, 4) significantly reduced by the addition of either ethylisopropylamiloride or DIDS to the bath, 5) significantly increased by a high bath K+ concentration, and 6) unchanged by the addition of Ba2+ to the bath. These data suggest that both Na+-coupled and Cl--coupled basolateral acid-base fluxes are involved in determining the rate of recovery of pH(i) after acidification. The most likely ones to be important in regulating pH(i) are a Na+/H+ exchanger and a Na+-coupled Cl-/ HCO3- exchanger. In birds, long-looped mammalian-type nephrons resemble short-looped transitional nephrons but differ markedly from superficial loopless reptilian-type nephrons.