Cell pH and luminal acidification in Necturus proximal tubule

Cellular potential and pH measurements (pHi) were carried out in the perfused kidney of Necturus on proximal tubules with standard and recessed-tip glass microelectrodes under control conditions and after stimulation of tubular bicarbonate reabsorption. Luminal pH and net bicarbonate reabsorption were measured in parallel experiments with recessed-tip glass or antimony electrodes, both during stationary microperfusions as well as under conditions of isosmotic fluid transport. A mean cell pH of 7.15 was obtained in control conditions. When the luminal bicarbonate concentration was raised to 25 and 50 mM, pH, rose to 7.44 and 7.56, respectively. These changes in pHi were fully reversible. Under all conditions intracellular H+ was below electrochemical equilibrium. Thus the maintenance of intracellular pH requires "active" H+ extrusion across one or both of the cell membranes. The observed rise in pHi and the peritubular depolarization after stimulation of bicarbonate reabsorption are consistent with enhanced luminal hydrogen ion secretion and augmentation of peritubular bicarbonate exit via an anion-conductive transport pathway.