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;), measured with the pH-sensitive fluorescent dye 2',7'-bis(2carboxyethyl)-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 NH4C1 pulse. The rate of recovery of pH, 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 Ba21 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, after acidification. The most likely ones to be important in regulating pHj are a Na⁺/H+ exchanger and a Na⁺-coupled C\~l HCOj exchanger. In birds, long-looped mammalian-type nephrons resemble short-looped transitional nephrons but differ markedly from superficial loopless reptilian-type nephrons. chickens; ammonium chloride pulse; intracellular acidification; intrinsic buffering capacity; sodium-coupled basolateral acid-baseiluxes; chloride-coupled basolateral acid-base fluxes