Regulation of intracellular pH (pH,) in avian proximal tubules

Regulation of pH is important in maintenance of normal cellular function and may play an important role in renal tubular transport of organic anions and cations, but no information is available on pH in avian proximal tubules. Therefore, we examined pH and its regulation in isolated, nonperfused proximal tubules of chicken intermediate nephrons. pH was measured by fluorescence ratio microscopy using the pH-sensitive fluorescent dye BCECF Resting pH under control conditions (HEPESbuffered avian medium; pH 7.4; 39°C) was 7.36 ±0.03 (mean ±SE). During exposure to NFUCl (20 mM) in the bath, pHi increased initially to 7.83 ±0.04 and then gradually decreased to 7.51 ±0.03 over the ensuing 2 min Removal of NFUCl from the bath resulted in rapid intracellular acidification to pH; of 6.81 ±0.04. At this time, intrinsic buffering capacity (β_i mM H⁺/pH U), rate of change of pH (dpH/dt, pH U/sec), NH? flux through the basolateral membrane (JNH3, nmol/cm /sec), and permeability of basolateral membrane to NH3 (Puns, X 10'3 cm/sec) were calculated to be 26.5 ±2.6, OA2±00&, 7.9 ±0.6, and 16.2 ±1.2. pH, recovery rates (X 10^-4 pH U/sec) after cell acidification by NtCl removal were 57 ±5 for control, 45 ±4 with 1 mM amiloride, 34 ±10 with 0.1 mM DIDS, 34 ±14 with Na⁺ removal (replacement with iV-methyl-D-glucamine chloride), 57 ± 5 with Cl^- removal (replacement with Na-gluconate). Whereas there was no effect of Cl removal alone, simultaneous removal of Na⁺ and Cl^- (replacement with sucrose) reduced the recovery rate by 75% almost twice the effect of Na⁺ removal alone. These data suggest that Na⁺/H⁺ exchange and possibly a synergistic effect of Cl^- regulate pHi at the basolateral membrane of avian renal proximal tubules. (NSF 9001985).