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

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Abstract
To examine the cellular mechanisms of H transfer, the [14C]DMO[5,5-dimethyl-2,4-oxazolidinedione]-derived cell pH was studied in rabbit separated renal proximal tubules. Under normal conditions, cell pH (7.508 .+-. 0.008, SE) was 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 Na resulted in cell acidification. Addition of 10-3 M ouabain to the medium dissipated the transmembrane Na gradient [Na]o/[Na]i and lowered cell pH. 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 alkalinization. In the proximal tubule the H transfer from cell to lumen may be active, whereas the HCO3 transfer across the basal membrane may be passive; there is evidence for a Na:H exchange via a countertransport mechanism; and Na:H exchange may not be the only mechanism responsible for active H transfer.

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