The acid-base affects on Na+ and Cl- transport across intestinal epithelia include CO2 effects on colonic absorption and pH effects on ileal absorption. Carbonic anhydrase activity and the provision of H+ and HCO3 - to apical membrane NHE3 and AE1 exchangers, respectively, contribute to this effect in the colon.
Recently, we reported that CO2 tension stimulates colonic (but not ileal) Na+ and Cl- absorption in large part by modulating the vesicular trafficking of NHE3 and AE1 to and from the apical membrane. We are currently examining: (i) the mechanisms by which CO2 tension modulates vesicular trafficking including the role of the cytoskeleton and Ca+2, (ii) the role of carbonic anhydrase and its inhibitors in vesicular trafficking, and (iii) the relation of other transporters (e.g., DRA) and Cl- secretion to this process. These studies are performed in cultured cells, isolated tissues, and intact animals, and include the use of isotopic and biochemical tracers, fluorescence and transmission electron microscopy, and molecular biological techniques.