Cell pH and acid transport in renal cortical tissue

Cell pH (pHc) was examined by the [14C]DMO technique in suspensions of proximal tubule fragments from rabbit renal cortex. In buffer with 10 mM HCO3(-), pHc was more alkaline than external pH (pHe) at values of the latter < 7.4. Maximal cell-to-extracellular pH gradients (delta pH) occurred at pHe = 6.8 and below. At pHe > 7.4, pHc was more acid than pHe was. However, pHc was always more alkaline than the electrochemical equilibrium pH. At pHe congruent to 7.0, 60 min of deoxygenation decreased delta pH from 0.22 +/- 0.02 to 0.05 +/- 0.01. Reoxygenation restored delta pH to control values. Incubation with ouabain abolished the delta pH. Both the carbonic anhydrase inhibitor, acetazolamide, and the anion transport inhibitor, 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS), increased delta pH. The studies demonstrate relative intracellular alkalinity in proximal tubule. A fall in pHc occurs with maneuvers that interfere with H+ pumping out of the cells. A rise in pHc occurs with maneuvers that interfere with the disposition of intracellular alkali: slowing of HCO3(-) generation with acetazolamide or blocking of HCO3(-) exit with SITS. The results support a H+-secretory model of proximal tubule acid transport that is dependent on maintenance and dispersal of intracellular alkalinity.