Intracellular pH (pH_i) in gastric surface epithelium is more susceptible to serosal than mucosal acidification

Intracellular microelectrode techniques were used to examine the effects of mucosal or serosal acidification on intracellular pH (pH_i) in gastric surface epithelial cells. Necturus antrum was mounted in a modified Ussing chamber, and pH_i was determined from the difference between the potentials recorded by intracellular conventional and pH-sensitive microelectrodes. In tissues bathed with bicarbonate-buffered Ringer's solution (pH 7), acidification of the mucosal solution to pH 4.5 by isotonic replacement of the NaHCO₃ with NaCl had no significant effects on pH_i. In contrast, acidification of the serosal solution to pH 4.5 by replacing the bicarbonate reduced pH_i from 7.32 ± 0.04 to 6.95 ± 0.06 (p < 0.001, n = 8). Similarly, in tissues bathed with HEPES-buffered Ringer's solution (pH 7.0), pH_i was unaffected by reducing the mucosal solution pH to 4.5 with HCl but fell 0.21 ± 0.05 pH units (p < 0.01, n = 7) during acidification of the serosal solution to pH 6. These results suggest that gastric epithelium is more sensitive to acidification from the serosal than the mucosal side. Such a finding is consistent with the concept of a gastric mucosal barrier to luminal acid. It may also explain the gastric epithelium's greater sensitivity to acute ulceration during systemic acidosis.