Basolateral regulation of pH(i) in isolated snake renal proximal tubules in presence and absence of bicarbonate

Intracellular pH (pH(i)) and its basolateral regulation were studied in isolated proximal-proximal and distal-proximal segments of garter snake (Thamnophis spp.) renal tubules with oil-filled lumens in HEPES-buffered and in HEPES-HCO₃/^--buffered media (pH 7.4 at 25°C). pH(i) was measured with the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5,6- carboxyfluorescein (BCECF) under resting conditions and in response to NH₄Cl pulse. Resting pH(i) (~7.1-7.2) and its response to and rate of recovery (dpH(i)/dt) from an NH₄Cl pulse were not affected by the presence or absence of HCO₃/^- in either segment. Rate of recovery was depressed by Na⁺ removal in distal-proximal segments only and only in HEPES buffer. It was not affected by removal of Cl^- or of both Na⁺ and Cl^- or by reduction in membrane potential through addition of Ba²⁺ (5 mM) or high K⁺ (75 mM) in either segment in either HEPES or HEPES-HCO₃/^- buffer. The Na⁺/H⁺ exchange inhibitor ethylisopropylamiloride (EIPA) (100 μM) and the anion exchange inhibitor DIDS (100 μM) reduced dpH(i)/dt in the distal-proximal segments only and only in HEPES-HCO₃ buffer. The H⁺-ATPase inhibitor bafilomycin (1 μM), H⁺-K⁺-ATPase and K⁺/NH₄/⁺ exchange inhibitor Schering 28080 (10-100 μM), organic cation efflux inhibitor tetrapentylammonium (25 μM-20 mM), and K⁺ channel blocker tetraethylammonium (20 mM) had no effect on dpH(i)/dt in either segment. These data do not clearly support basolateral regulation of pH(i) in snake proximal renal tubules by commonly recognized Na⁺-dependent or Na⁺- independent acid or base transporters.