Taurodeoxycholate modulates apical Cl-/OH- exchange activity in Caco2 cells

Area of Science:

• Gastroenterology
• Cell Biology
• Molecular Biology

Background:

• Bile acid malabsorption is linked to diarrhea in conditions like ileal resection and Crohn's disease.
• The precise mechanisms of bile acid-induced diarrhea, particularly effects on intestinal chloride transport, remain unclear.
• Previous research focused on colonic chloride secretion, leaving apical intestinal chloride absorption less defined.

Purpose of the Study:

• To investigate the impact of bile acids on the apical chloride/hydroxyl (Cl(-)/OH(-)) exchange process.
• To utilize Caco2 cell monolayers as an in vitro model for studying these effects.
• To elucidate the specific signaling pathways involved in bile acid-mediated inhibition of Cl(-)/OH(-) exchange.

Main Methods:

• Caco2 cell monolayers were used as an in vitro model.
• Apical Cl(-)/OH(-) exchange activity was measured using pH gradient-driven (36)Cl uptake, assessing DIDS sensitivity.
• Cells were exposed to specific bile acids (taurodeoxycholate, glycochenodeoxycholate) and inhibitors (BAPTA-AM, chelerythrine chloride, LY294002, RpcAMP).

Main Results:

• Short-term exposure to taurodeoxycholate (TDC) and glycochenodeoxycholate (GCDC) significantly inhibited apical Cl(-)/OH(-) exchange by 60-70%.
• Inhibition by TDC was dependent on calcium (Ca(2+)) and mediated by protein kinase C beta I (PKC beta I) activation.
• The effect was also dependent on PI3 kinase but not protein kinase A (PKA).

Conclusions:

• Bile acids directly inhibit human intestinal apical Cl(-)/OH(-) exchange activity.
• This inhibition occurs through Ca(2+)-, PI3 kinase-, and PKC beta I-dependent signaling pathways.
• Findings provide crucial insights into the cellular mechanisms underlying bile acid-induced diarrhea.