Hydrogen transport in rabbit kidney proximal tubules--Na:H exchange

In order to examine the cellular mechanisms of H transfer, we studied the [14C]DMO-derived cell pH in rabbit separated renal proximal tubules. Under normal conditions, cell pH (7.508 +/- 0.008, SE) was found to be more alkaline than medium pH (7.404 +/- 0.009, SE). The [14C]DMO-derived cell pH was not affected either by 10(-2) M unlabeled DMO or 10(-3) M probenecid. Removal of external sodium resulted in cell acidification. Addition or 10(-3) M ouabain to the medium dissipated the transmembrane sodium gradient [Na]o/[Na]i and lowered cell pH. However, the DMO-derived cell pH observed in the presence of ouabain was higher than the calculated cell pH, assuming passive distribution of H ions across the cell membrane. In the presence of ouabain, reducing [Na]o/[Na]i led to cell acidification, and augmenting [Na]o/[Na]i caused cell alkalinization. These results indicate that in the proximal tubule: 1) the H transfer from cell to lumen is active, whereas the HCO3 transfer across the basal membrane may be passive; 2) there is evidence for a Na:H exchange via a countertransport mechanism; and 3) Na:H exchange may not be the only mechanism responsible for active H transfer.