Demonstration of a pH gradient across mucus adherent to rabbit gastric mucosa: evidence for a 'mucus-bicarbonate' barrier.

We examined the ability of the mucus layer adherent to isolated pieces of rabbit gastric mucosa to maintain a pH gradient across it. Using antimony microelectrodes, a stable pH gradient was detected from pH 2.31 +/- 0.04 on the luminal side to pH 7.26 +/- 0.15 (n = 22) on the epithelial side of the mucus layer. The gradient was maintained for at least 60 minutes. A metabolic inhibitor, potassium cyanide, markedly reduced the tissues' ability to maintain this pH gradient, suggesting involvement of an active cellular process, probably that of bicarbonate secretion. These observations provide additional evidence in favour of a 'mucus-bicarbonate' barrier which may be of importance in protecting the underlying gastric mucosa.