Role of passive HCO3(-)-diffusion in duodenal acid-stimulated alkaline secretion

We investigated acid-stimulated alkaline secretion (AS) under different luminal acid concentrations and its relation to mucosal damage on isolated proximal rabbit duodenal mucosa. Luminal HCl caused an increase of AS depending on their concentration, and it was not specific for acid, but occurs also with luminal ethanol. Histology showed [H+]-dependent mucosal damage ranging from villus tip lesions to deep mucosal injury. Ouabain- and/or anoxia-sensitive (active) AS constituted 80% and 100% respectively of basal AS. After exposure to various luminal acid concentrations passive diffusion (sensitive only to removal of nutrient HCO3-) was solely responsible for the rise in AS. We conclude that in the in vitro rabbit duodenum passive diffusion of HCO3- associated with increasing mucosal damage is the major component of the rise in AS.