Influence of luminal acidification on bicarbonate transport by gastric and duodenal isolated mucosae.

Transport of HCO3- was measured by pH-stat titration in pairs of amphibian fundic or proximal duodenal mucosa using a modified Ussing chamber. Separate unbuffered solutions bathed the luminal sides of two tissues while their serosal surfaces were in contact with a common buffered solution. Lowering luminal pH bathing one fundic mucosa from 7.40 to 1.85 significantly increased HCO3- transport by another fundus. However, acidification of fundic mucosa did not affect duodenal HCO3- transport. In duodenal mucosal pairs, lowering pH from 7.40 to 5.46 caused an increase in HCO3- transport by the other tissue. Luminal H+ ion concentration may therefore regulate HCO3- transport via a humoral mechanism.