Studies of the pH gradient across gastric mucus.

We studied the possibility that gastric mucosa protects itself from luminal acid by maintaining a neutral zone adjacent to the mucosa. In the anaesthetised rat pedicles of gastric fundus mucosa with an intact mucus layer were studied. Using pH sensitive antimony chloride microelectrodes, we demonstrated a maximal pH adjacent to the mucosa of 6.68 when luminal pH was 2 (n = 30). The intramucus pH was compromised when luminal acidity was greater than pH 1.5. Addition of 10 mM aspirin or 5% N-acetyl cysteine to the luminal solution also caused a fall in intramucus pH. Sodium taurocholate (10 mM) caused a physical change in the appearance of the mucus which became brittle and fragmented. The pH within the mucus layer fell as a result of this fragmentation. 16, 16 dimethyl prostaglandin E2 prevented the fall in intramucus pH produced by 20 mM aspirin. Similar results were obtained in specimens of human gastric mucosa removed at gastrectomy. These observations suggest that an alkaline zone is maintained within the mucus layer adjacent to the gastric epithelium which may have an important protective role.