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 (pHi), measured with the pH-sensitive fluorescent dye 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, was ∼7.3 under control conditions (HEPES-buffered medium with pH 7.4 at 37°C) and was reduced to ∼7.0 in response to NH4Cl pulse. The rate of recovery of pHi 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 pHi after acidification. The most likely ones to be important in regulating pHi are a Na+/H+exchanger and a Na+-coupled Cl−/ HCO 3 − exchanger. In birds, long-looped mammalian-type nephrons resemble short-looped transitional nephrons but differ markedly from superficial loopless reptilian-type nephrons.