Anion transport regulates intracellular pH in renal cortical tissue

The regulation of cell pH by anion transport was examined in suspensions of rabbit renal proximal tubules. Values for cell pH were derived from 14C-labeled 5,5-dimethyloxazolidine-2,4-dione distribution. In buffer with 10 mM/l HCO3-- and gassed with 95% O2/5% CO2, the anion transport inhibitors, 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene and furosemide, raised the cell-to-extracellular pH gradient from 0.23 +/- 0.02 to 0.31 +/- 0.02 and 0.31 +/- 0.03, respectively, but in combination their effects were not additive. Replacement of extracellular Cl-- by NO3-- raised the pH gradient from 0.24 +/- 0.04 to 0.37 +/- 0.05. Neither inhibitor raised the pH gradient in Cl-- -free media. Incubation of suspensions in HCO3-- and CO2-free media raised the pH gradient from 0.18 +/- 0.02 to 0.29 +/- 0.03. Removal of Cl-- in addition to HCO3-- and CO2 raised the pH gradient still further, to 0.36 +/- 0.02. The results demonstrate that two different anion transport inhibitors raise cell pH and the cell-to-extracellular pH gradient in proximal tubules and are consistent with the idea that the mechanism for this effect is inhibition of alkali anion exit from the tubule cell. This process appears to depend on extracellular Cl-- and probably occurs primarily by HCO3-- transport. The results support the concept that alkali anion transport, most probably HCO3-- exit from the peritubular cell border, is an important regulator of cell pH in renal proximal tubule.