Effect of luminal acid on intracellular pH in oxynticopeptic cells in intact frog gastric mucosa.

The effect of changes in luminal [H+] on intracellular pH in oxynticopeptic cells was examined using intact sheets of frog (Rana catesbeiana) gastric mucosa in which oxynticopeptic cells were selectively loaded with the pH-sensitive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). The serosal solution was buffered with either HCO3- or N-2-hydroxymethylpiperazine-N'-2-ethanesulfonic acid (HEPES). Luminal pH was decreased from 7.2 to 1.5 and changed back to 7.2. In stimulated (forskolin-treated) tissues, intracellular pH decreased at luminal pH 1.5 only in HEPES, with complete recovery at 7.2. In resting (omeprazole-treated) tissues, intracellular pH began to decrease at luminal pH 2.0 in HEPES and at 1.5 in HCO3-, with complete recovery at 7.2 in both. In resting tissues bathed in Cl(-)-free HEPES, the recovery of intracellular pH at luminal pH 7.2 was completely prevented by serosal amiloride (1 mmol/L) but was not affected by serosal 4,4'-diisothiocyanatodihydrostilbene-2-2'-disulfonic acid (H2-DIDS; 0.5 mmol/L). In resting tissues bathed in Cl(-)-free HCO3-, the recovery of intracellular pH at luminal pH 7.2 was not affected by amiloride but was prevented partially by H2-DIDS and completely by combination of H2-DIDS and amiloride or by removal of ambient Na+. These results suggest that during exposure to high luminal [H+]: (a) stimulated oxynticopeptic cells maintain a steady intracellular pH more readily than resting cells; (b) serosal HCO3- protects oxynticopeptic cells from intracellular acidosis; and (c) both Na+/H+ exchange and Na(+)-HCO3- cotransport are involved in the recovery from intracellular acidosis in resting oxynticopeptic cells.