Functional characterization of Cl^-/HCO₃^- exchange in villous cells of the mouse ileum

抄録

At least three kinds of Cl^-/HCO₃^- exchangers, SLC26A3, SLC26A6 and AE2, have been demonstrated to be expressed in the intestinal epithelial cell. To examine the functional expression of these exchangers in the native enterocyte, we studied the Cl^-/HCO₃^-- exchange activity in isolated villi from the mouse ileum by microfluorometric intracellular pH (pH_i) measurement. The pH_i value increased upon Cl^- removal when the villus was superfused with an HCO₃^-/CO₂-buffered solution, while the response was blunted when superfused with an HCO₃^-/CO₂-free, Hepes-buffered solution. The recovery of pH_i value induced by Cl^- re-addition (after initial Cl^- removal) was totally or partially mimicked by the addition of Br^-, I^-, F^-, NO₃^-, or SO₄^2- (in the absence of Cl^-). The increase in pH_i value induced by Cl^- removal was partially inhibited in the presence of DIDS (30 μM), tenidap (10 μM), niflumic acid (30 μM) or NPPB (30 μM). Increasing the K⁺ concentration from 5 mM to 60 mM in the superfusion solution induced a reversible increase in pH_i value under the HCO₃^-/CO₂-buffered condition, while it had hardly any effect on pH_i under the Hepesbuffered condition. The K⁺-induced pH_i changes were partially suppressed by removing Cl^- from the superfusion solution. These results, together with the reported findings of mouse slc26a3, slc26a6 and AE2 in heterologously expressed systems, suggest the possibility that these three exchangers may all be functionally expressed in mouse ileal villous cells.