Effects of inhibition of epithelial ion transport and carbonic anhydrase on CO 2 ‐induced intracellular acidification in mouse duodenal villous cells

Epithelial ion transporters and carbonic anhydrase (CA) participate in the regulation of intracellular pH (pH i ) in duodenal villous cells. Luminal acid or elevated luminal pCO 2 (CO 2 stress) acidifies duodenal epithelial cells. The Na/H exchange‐1 (NHE‐1) inhibitor dimethyl amiloride (DMA) or the Na:HCO 3 − cotransport (NBC) inhibitor DIDS enhances cellular acidification, whereas the CA inhibitors methazolamide (MTZ) or benzolamide (BNZ) abrogates acidification. We examined the effects of these inhibitors on pH i under CO 2 stress in mouse duodenum. Mouse duodenal villous cells were exposed and loaded with a pH‐sensitive fluorescence dye BCECF, and pH i was measured with in vivo fluorescent microscope. Duodenal mucosa was exposed to high CO 2 solution (pH 6.4, pCO 2 260 Torr) with or without DMA (0.1 mM), DIDS (1 mM), MTZ (1 mM), BNZ (1 μM) or novel cell‐impermeant CA inhibitor sulfonamide compounds. CO 2 − stress rapidly acidified the cells followed by pH i recovery to the baseline after CO 2 removal. DMA enhanced CO 2 ‐induced pH i decrease, whereas DIDS and MTZ reduced the acidification. BNZ and the cell‐impermeant CA inhibitors had no effect. The divergent effects of DMA and DIDS on pH i suggest that NHE‐1 is more important than is NBC for pH i regulation. Compared with complete inhibition of CO 2 − induced acidification by MTZ or BNZ in rat duodenum, MTZ was less effective, and the impermeant CA inhibitors had no effect in mouse duodenum, consistent with a marked species difference between rat and mouse for pH i regulation by CA and by plasma membrane acid‐base transporters.