BARRIER FUNCTION OF THE GASTRIC MUCUS GEL

The gastric epithelium is covered by a continuous layer of secreted mu cus and bicarbonate. The function of this mucobicarbonate layer in ter ms of protecting the epithelial cells from luminal acid is controversi al. Several studies conducted in vitro have shown that gastric mucus c an slow proton diffusion and can enable the formation of a pH gradient across the mucobicarbonate layer. In our laboratory, simultaneous mea surements of intracellular pH and the thickness of the mucus gel overl ying gastric surface cells in vivo indicated that surface cell acidifi cation rates and mucus gel thickness were inversely related. This sugg ests that the gastric mucobicarbonate layer delays proton permeation i nto gastric surface cells, enabling secreted bicarbonate to neutralize luminal acid. Several theoretical models, including the effects of mu cus and bicarbonate secretion, convection, stirring, and Lipids are of fered as a possible explanation for the experimental observations. Lip id content and additional unstirred layers outside of the mucus gel ar e offered as possible explanations for the experimental observations. On the basis of the available data and theoretical considerations, we can conclude that all of these factors probably interact in an integra ted manner to protect the gastric epithelial cells from damage due to luminal acid.