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

We examined pH_i and its regulation in isolated nonperfused proximal tubules of chicken loopless nephrons (70-90% of nephrons in kidney) using pH-sensitive fluorescent dye BCECF. Under control conditions (HEPES buffer, pH 7.4; 37°C) resting pH was 7.18 ± 0.02 (mean ± SE). Addition of 20 mM NH₄Cl to bath increased pH to 7.68 ± 0.03. Removal of NH₄Cl from bath reduced pH to 6.95 ± 0.03. Rate of pH_i change (dpH_i/dt, pH U/s), intrinsic buffering capacity (β_i, mM H⁺/pH U), basolateral NH₃ flux (J_NH3, nmol/cm²/s), and basolateral NH₃ permeability (P_NH3, cm/s × 10^-3) were, respectively: 0.13 ± 0.01, 27.55 ± 3.42, 1.86 ± 0.16, and 3.80 ± 0.32. Control recovery rate (dpH_i/dt) from acid pH_i after NH₄Cl removal was 4.98 ± 0.38 × 10^-3 pH U/s. This dpH_i/df was significantly (P < 0.05; paired studies) decreased by removal of Na⁺ (replacement with N-methyl-D-glucamine Cl^-), simultaneous removal of Na⁺ and Cl^- (replacement with N-methyl-D-glucamine-gluconate), or addition of DIDS, significantly increased by high K⁺ (75 mM) (depolarization of basolateral membrane); and unchanged by removal of Cl^- (replacement with Na⁺-gjuconate) or addition of EIPA (1 mM) or Ba²⁺ (basolateral depolarization; blockage of K⁺ channels) Resting pH was significantly (P < 0.05; paired studies) decreased by Na⁺ removal or simultaneous Na⁺ and Cl^- removal; significantly increased by high K⁺; and unchanged by Cl^- removal alone or addition of Ba²⁺. Data do not fit concept of pH_i regulation by usual basolateral transporters (Na⁺/H⁺ exchange; Na⁺-dependent and Na⁺-independent Cl^- /HCO₃^- exchange; or Na⁺-HCO₃^--CO₃^2- cotransporter). There may be Na^--HCO₃ cotransporter for basolateral HCO₃^- entry.