Chapter 8 Anion absorption in the intestine: Anion transporters, short-chain fatty acids, and role of the DRA gene product

Modulation of butyrate transport in Caco-2 cells

The aim of this study was to investigate the putative influence of some pharmacological agents and drugs of abuse upon the apical uptake of butyrate (BT) into Caco-2 cells. The apical uptake of (14)C-BT by Caco-2 cells was (1) time and concentration dependent, (2) pH dependent, (3) Na(+) independent and Cl(-) dependent, (4) energy dependent, (5) inhibited by several BT structural analogues (acetate, propionate, alpha-ketobutyrate, pyruvate, lactate), (6) insensitive to the anion exchange inhibitors DIDS and SITS and (7) inhibited by the monocarboxylate transport (MCT) inhibitors NPPB and pCMB. These characteristics are compatible with an involvement of MCT1-mediated transport. Acutely, uptake of a low concentration of (14)C-BT (10 microM) was reduced by acetaldehyde, acetylsalicylic acid, indomethacin, caffeine and theophylline and increased by MDMA. Chronically, uptake was increased by caffeine and decreased by tetrahydrocannabinol and MDMA; reverse transcription quantitative real-time PCR analysis showed that these three compounds decreased the mRNA levels of MCT1. Acutely, acetaldehyde, indomethacin and MDMA reduced the uptake of a high concentration of (14)C-BT (20 mM), and acetylsalicylic acid increased it. Chronically, none of the compounds affected uptake. Acetaldehyde, indomethacin and propionate seem to be competitive inhibitors of (14)C-BT uptake. Acetylsalicylic acid simultaneously increased the K (m) and the V (max) of (14)C-BT uptake. In conclusion, MCT1-mediated transport of (14)C-BT in Caco-2 cells is modulated by either acute or chronic exposure to some pharmacological agents and drugs of abuse (acetaldehyde, acetylsalicylic acid, indomethacin, caffeine, theophylline and the drugs of abuse tetrahydrocannabinol and MDMA).

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

At least three kinds of Cl(-)/HCO(3)(-) 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(-)/HCO(3)(-)- 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 HCO(3)(-)/CO(2)-buffered solution, while the response was blunted when superfused with an HCO(3)(-)/CO(2)-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(-), NO(3)(-), or SO(4)(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 muM), tenidap (10 muM), niflumic acid (30 muM) or NPPB (30 muM). Increasing the K(+) concentration from 5 mM to 60 mM in the superfusion solution induced a reversible increase in pH(i) value under the HCO(3)(-)/CO(2)-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.