Intracellular pH in the isolated perfused rabbit proximal straight tubule

For the purpose of measuring the intracellular pH (pHi) of the mammalian renal proximal tubule, a liquid membrane pH microelectrode was made using a neutral hydrogen ion-selective carrier. The pHi of the rabbit proximal straight tubule perfused in vitro with a solution containing 25 mM HCO3- was 7.22 +/- 0.03. We noted a value significantly lower than the bath pH of 7.44 +/- 0.02 but significantly higher than the pHi of 6.62 +/- 0.03 predicted for passive H+ distribution. Replacement of luminal Na+ with choline quickly (within 1 min) decreased pHi from 7.25 +/- 0.05 to 7.10 +/- 0.05 (P less than 0.001). This change was reversible when Na+ was added again in the luminal solution. A reduction of luminal Na+ from 20 mM to 0 also reduced pHi from 7.15 +/- 0.06 to 7.04 +/- 0.08, and this pHi reduction was blocked by luminal addition of 1 mM amiloride. However, pHi reduction induced by luminal Na+ removal was not affected by luminal addition of 1 mM SITS. Replacement of bath Na+ with choline also reversibly reduced pHi from 7.27 +/- 0.02 to 7.15 +/- 0.02 (P less than 0.001), but this change was totally blocked by the presence of 1 mM SITS. Accordingly, these data suggest that a Na+-H+ exchanger exists in the luminal membrane of the intact rabbit proximal straight tubule.