ENHANCED H+ DIFFUSION BY NH4+ HCO3- - IMPLICATIONS FOR HELICOBACTER-PYLORI-ASSOCIATED PEPTIC-ULCERATION/

The in vitro effect of ammonium bicarbonate buffer on mucus H+ permeab ility is reported here. The diffusional resistance of mucus and water was demonstrated to be dependent on buffer concentration, and the cont rast between the two types of layers was most pronounced for low buffe r concentration near neutrality. Moreover, the pK(a) values of HCO3- a nd NH3 had a profound effect on measured D(HCl). These in vitro studie s suggest that a potentially damaging high local concentration of NH3 and HCO3- within the mucus layer generated by the action of Helicobact er pylori urease on endogenous intragastric urea could greatly acceler ate proton flux to the surface epithelium by operation of a buffer shu ttle. This results in enhanced H+ permeability, particularly at pK(a) values of HCO3- and NH3, and that in extreme circumstances this may re sult in gastric ulcer formation.