TRANSEPITHELIAL TRANSPORT OF CHOLYLTAURINE BY CACO-2 CELL MONOLAYERS IS SODIUM-DEPENDENT

Bile acids are efficiently recovered from the intestinal lumen by a Na+-dependent transport process that is localized in the ileal enterocyte brush-border membrane. To establish a cell culture model for this process, we examined the Na+ dependence of cholyltaurine (C-tau; taurocholate) transport across monolayers of differentiated Caco-2 cells grown on permeable filter inserts. Transport of [H-3]C-tau was Na+ dependent (>20-fold stimulation), saturable, and time linear for at least 60 min. The apparent Michaelis constant of [H-3]C-tau transport was approximately 65 muM, and the maximal transport rate was approximately 800 pmol . min-1 . mg protein-1. Transport of [H-3]C-tau in the apical-to-basolateral direction was 17-fold greater than transport in the reverse direction. Lowered incubation temperature, various metabolic inhibitors, and various unlabeled bile acids inhibited [H-3]C-tau transport. Caco-2 cells thus transport bile acids in a manner similar to that described for ileal brush-border membrane vesicles and isolated ileal enterocytes and are therefore an appropriate model for studying the molecular basis of ileal bile acid transport.