Bile acid-induced secretion in polarized monolayers of T84 colonic epithelial cells: Structure-activity relationships.

Bile acid epimers and side-chain homologues are present in the human colon. To test whether such bile acids possess secretory activity, cultured T84 colonic epithelial cells were used to quantify the secretory properties of synthetic epimers and homologues of deoxycholic acid (DCA) and chenodeoxycholic acid (CDCA). In our study, chloride secretion was measured as changes in short-circuit current (DeltaI(sc), in microA/cm2) with the use of voltage-clamped monolayers of T84 cells mounted in Ussing chambers. Bile acids were added at 0.5 mM, a concentration that did not alter transepithelial resistance. Data were expressed as peak DeltaI(sc) (means +/- SD). When added bilaterally, DCA stimulated a DeltaI(sc) response of 15.7 +/- 12.5 microA/cm2. The 12beta-OH epimer of DCA was less potent (DeltaI(sc) = 8.0 +/- 1.7 microA/cm2), whereas its 3beta-OH epimer had no effect. CDCA stimulated secretion (DeltaI(sc) = 8.2 +/- 5.5 microA/cm2), whereas both its 7beta-OH and 3beta-OH epimers were inactive, as was lithocholic acid. HomoDCA (1 additional side-chain carbon) was active (DeltaI(sc) = 7.8 +/- 4.8 microA/cm2), whereas norDCA (1 fewer carbon) and dinorDCA (2 fewer carbons) were not. Taurine conjugates of DCA and CDCA stimulated secretion (DeltaI(sc) = 12.3 +/- 7.5 and 8.8 +/- 4.8 microA/cm2, respectively) from the basolateral side but not the apical side. Uptake of taurine conjugates from the basolateral but not the apical side was shown by mass spectrometry. These studies indicate marked structural specificity for bile acid-induced chloride secretion and show that modification of bile acid structure by colonic bacteria modulates the secretory properties of these endogenous secretagogues.