Regulatory mechanism of cell pH in the renal proximal tubule of bullfrog nephron.

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Abstract
To examine the cellular mechanism of urinary acidification in detail, micropuncture studies were performed on the in situ bullfrog proximal tubule with nigericin-based pH microelectrodes. Pencil-type double-barreled antimony microelectrodes were also used for monitoring pHs of the tubular fluids. Luminal perfusion of 10-3 M cyanide caused a biphasic change in cell pH (pHi): i.e., early acidification by 0.04 pH unit in 2 min and later alkalinization by 0.04. A profound depolarization of 30-35 mV was observed in the peritubular membrane potential (EM Peri), although the tubular fluid pH (pHTF) was elevated by 0.11 unit. Luminal substitution of 100 mM Na+ by Li+ acidified the cell by 0.06 pH unit with a depolarization of EM Peri by 8 mV and an alkalinization of pHTF by 0.01 unit. It is a fact that cellular acidification and luminal alkalinization are in good agreement with the depression of luminal H+ secretory mechanism. Perfusion of 10-4 M SITS from the peritubular side caused a rise in pHi by 0.04 without appreciable changes in EM Peri in the short period application. Peritubular perfusion of 10-4 ouabain lowered the pHi by 0.07 with a resulting depolarization of EM Peri by 15.4 mV, meanwhile, the pHTF, while initially lowered by 0.07 unit, was elevated 4 min later by 0.12. Inhibitions of the peritubular ion transport mechanism caused some pH changes in the same direction, both in the cell interior and the tubular fluid. Further, from the ouabain experiment, it is inferred that some linkages, mediated by Na+ and H+ (or HCO3-), would exist between the peritubular and luminal membranes.