Effect of CO2 on pHi in rabbit parietal, chief, and surface cells

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Abstract
We investigated the pH recovery mechanisms in rabbit parietal, chief, and surface cells during pH shifts induced by introduction or removal of exogenous CO2-HCO3-. Intracellular pH (pHi) was measured using the fluorescent dye 2'',7''-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Gastric cells were highly purified by density gradient centrifugation and elutriation. When cells suspended in N-2-hydroxyethylpiperazene-N''-2-ethanesulfonic acid (HEPES)-100%O2, extracellular pH (pHo) 7.4, were exposed to 24 mM HCO3--5% CO2, pHo 7.2, all cells quickly acidified by 0.3-0.4 pH units. Almost complete pH-recovery was dependent on the presence of extracellular Na+ (Nao+) and was blocked by 1 mM amiloride. The Na+-independent recovery was blocked by intracellular Cl- depletion or by 0.4 mM 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid (DIDS). In chief cells and surface cells no recovery occurred in the absence of Nao+, and 1 mM amiloride blocked pH recovery in Na+-containing buffer. On removal of HCO3--CO2, the cells alkalinized, and subsequent pH recovery was fast, substantially extracellular Cl- (Clo-) and DIDS inhibitable in parietal cells but slow and Clo--independent in chief and surface cells. These results suggest that during intracellular acidification the Na+-H+ exchanger is the major pH regulator in these three gastric cell types even in the presence of HCO3-. During alkalinization the Cl--HCO3-(OH-) exchanger is the predominant pH recovery mechanism in parietal, but not in chief and surface cells. In parietal cells, this exchanger is also involved in recovery from acidification.