Dynamic regulation of gastric surface pH by luminal pH

In vivo confocal imaging of the mucosal surface of rat stomach was used to measure pH noninvasively under the mucus gel layer while simultaneously ima ging mucus gel thickness and tissue architecture. When tissue was superfuse d at pH 3, the 25 mu m adjacent to the epithelial surface was relatively al kaline (pH 4.1 +/- 0.1), and surface alkalinity was enhanced by topical dim ethyl prostaglandin E-2 (pH 4.8 +/- 0.2). Luminal pH was changed from pH 3 to pH 5 to mimic the fasted-to-fed transition in intragastric pH in rats. U nder pH 5 superfusion, surface pH was relatively acidic (pH 4.2 +/- 0.2). T his surface acidity was enhanced by pentagastrin (pH 3.5 +/- 0.2) and elimi nated by omeprazole, implicating parietal cell H,K-ATPase as the dominant r egulator of surface pH under pH 5 superfusion. With either pH 5 or pH 3 sup erfusion (a) gastric pit lumens had the most divergent pH from luminal supe rfusates; (b) qualitatively similar results were observed with and without superfusion flow; (c) local mucus gel thickness was a poor predictor of sur face pH values; and (d) no channels carrying primary gastric gland fluid th rough the mucus were observed. The model of gastric defense that includes a n alkaline mucus gel and viscous fingering of secreted acid through the muc us may be appropriate at the intragastric pH of the fasted, but not fed, an imal.