The possible role of bicarbonate in mucosal protection and peptic ulceration.

The surface epithelial cells of the gastroduodenal mucosa are thought to be protected from the damaging effects of acid by a covering layer of mucus into which is secreted bicarbonate. It is proposed here that mucus acts as a true barrier to hydrogen ion diffusion, and that the role played by bicarbonate is to adjust mucus pH to a range at which this barrier property is optimized. It is further proposed that a high content of luminal bicarbonate will promote the transfer of protons across mucus by a buffer shuttle mechanism, and that this may be the basis for the development of peptic ulceration.