REGULATION OF INTRACELLULAR PH IN PROXIMAL TUBULES OF AVIAN LONG-LOOPED MAMMALIAN-TYPE NEPHRONS

In nonperfused proximal tubules isolated from chicken long-looped mamm alian-type nephrons, intracellular pH (pH(i)), measured with the pH-se nsitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluoresc ein, was similar to 7.3 under control conditions (HEPES-buffered mediu m with pH 7.4 at 37 degrees C) and was reduced to similar to 7.0 in re sponse to NH4Cl pulse. The rate of recovery of pH(i) from this level t o 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 bat h, 4) significantly reduced by the addition of either ethylisopropylam iloride or DIDS to the bath, 5) significantly increased by a high bath K+ concentration, and 6) unchanged by the addition of Ba2+ to the bat h. These data suggest that both Na+-coupled and Cl--coupled basolatera l acid-base fluxes are involved in determining the rate of recovery of pH(i) after acidification. The most likely ones to be important in re gulating pH(i) are a Na+/H+ exchanger and a Na+-coupled Cl-/ HCO3- exc hanger. In birds, long-looped mammalian-type nephrons resemble short-l ooped transitional nephrons but differ markedly from superficial loopl ess reptilian-type nephrons.