Basolateral regulation of pHiin isolated snake renal proximal tubules in presence and absence of bicarbonate.

Intracellular pH (pHi) 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-[Formula: see text]-buffered media (pH 7.4 at 25°C). pHi 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 pHi (∼7.1-7.2) and its response to and rate of recovery (dpHi/d t) from an NH4Cl pulse were not affected by the presence or absence of[Formula: see text] 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-[Formula: see text] buffer. The Na+/H+exchange inhibitor ethylisopropylamiloride (EIPA) (100 μM) and the anion exchange inhibitor DIDS (100 μM) reduced dpHi/d tin the distal-proximal segments only and only in HEPES-[Formula: see text] buffer. The H+-ATPase inhibitor bafilomycin (1 μM), H+-K+-ATPase and K+/[Formula: see text]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 dpHi/d tin either segment. These data do not clearly support basolateral regulation of pHi in snake proximal renal tubules by commonly recognized Na+-dependent or Na+-independent acid or base transporters.