Effect of chronic inflammation on ileal short-chain fatty acid/bicarbonate exchange.

Short-chain fatty acids (SCFA) have been demonstrated to at least partially ameliorate chronic intestinal inflammation. However, whether and how intestinal SCFA absorption may be altered during chronic intestinal inflammation is unknown. A rabbit model of chronic ileitis produced by coccidia was used to determine the effect of chronic inflammation on ileal SCFA/HCO(-)(3) exchange. SCFA/HCO(-)(3) exchange was present in the brush-border membrane (BBM) of villus but not crypt cells from normal rabbit ileum. An anion-exchange inhibitor, DIDS, significantly inhibited SCFA/HCO(-)(3) exchange. Extravesicular Cl(-) did not alter the uptake of SCFA, suggesting that SCFA/HCO(-)(3) exchange is a transport process distinct from Cl(-)/HCO(-)(3) exchange. In chronically inflamed ileum, SCFA/HCO(-)(3) exchange was also present only in BBM of villus cells. The exchanger was sensitive to DIDS and was unaffected by extravesicular Cl(-). However, SCFA/HCO(-)(3) exchange was significantly reduced in villus cell BBM vesicles (BBMV) from chronically inflamed ileum. Kinetic studies demonstrated that the maximal rate of uptake of SCFA, but not the affinity for SCFA, was reduced in chronically inflamed rabbit ileum. These data demonstrate that a distinct SCFA/HCO(-)(3) exchange is present on BBMV of villus but not crypt cells in normal rabbit ileum. SCFA/HCO(-)(3) exchange is inhibited in chronically inflamed rabbit ileum. The mechanism of inhibition is most likely secondary to a reduction in transporter numbers rather than altered affinity for SCFA.