Regulation of intracellular pH in proximal tubules of avian loopless reptilian-type nephrons

In proximal tubules isolated from chicken superficial loopless reptilian-type nephrons, intracellular pH (pH(i)), measured with pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein, was ~7.1- 7.2 under control conditions (N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered medium with pH 7.4 at 37°C), and was reduced to ~6.9 in response to NH₄Cl pulse. The rate of recovery of phi (control value ≃ 5 x 10^-3 pH U/s) from this acid level was 1) significantly decreased by removal of Na⁺ or both Na⁺ and Cl^- from the bath or addition of 4,4'- diisothiocyanostilbene-2,2'-disulfonic acid (0.25 mM) to the bath, 2) significantly increased by high bath K⁺ (75 mM), and 3) unchanged by removal of Cl^- alone from the bath or addition of ethylisopropylamiloride (1 mM) or Ba²⁺ (5 mM) to the bath. Resting pH(i) was 1) significantly decreased by Na⁺ or simultaneous Na⁺ and Cl^- removal, 2) significantly increased by high K⁺, and 3) unchanged by Cl^- removal alone or addition of Ba²⁺. The data do not fit the concept of pHi regulation by the most commonly suggested basolateral transporters (Na⁺/H⁺ exchanger, Na⁺ -dependent and Na⁺- independent Cl^-/HCO₃/^- exchangers, or Na⁺-HCO₃/^- -CO₃/^2- cotransporter).