Na-HCO3 cotransport in rabbit parietal cells

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Abstract
Na- and HCO3-coupled recovery of intracellular pH (pHi) after acid loading was demonstrated in rabbit parietal cells. Intracellular pH of individual resting (i.e., cimetidine treated) parietal cells was continuously measured using microspectrofluorometry of the pH sensitive dye 2'',7''-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, acetoxymethylester. Parietal cells were acidified utilizing NH4Cl or by lowering external pH to 6.2. By means of either technique pHi decreased from 7.1 to 6.6. In solutions containing 1 mM amiloride, which blocked Na-H exchange, pHi recovered only if Na and HCO3 were both present. This amiloride-resistant, Na- and HCO3-dependent pHi recovery was inhibited by 100 .mu.M H2 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid (reversibly) and occurred at equal rates in Cl containing and Cl-free solutions. In NaCl solutions buffered with HCO3-CO2 and containing amiloride, after an acid load with HCO3 CO2 and containing amiloride after an acid load pHi recovers to pHi 7.0-7.1 solely through the activity of the Na-HCO3 cotransporter. Therefore, resting parietal cells appear to have a Na-HCO3 cotransporter that serves as a base loader under physiological conditions.

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