Evidence for an anion exchange mechanism for uptake of conjugated bile acid from the rat jejunum

Absorption of conjugated bile acids from the small intestine is very. effic ient. The mechanisms of jejunal absorption are not very well understood. Th e aim of this study was to clarify the mechanism of absorption of conjugate d bile acid at the apical membrane of jejunal epithelial cells. Brush-borde r membrane vesicles from intestinal epithelial cells of the rat were prepar ed. Absorption of two taurine-conjugated bile acids that are representative of endogenous bile acids in many variate vertebrate species were studied. In ileal, but not jejunal brush-border membrane vesicles, transport of conj ugated bile acids was cis-stimulated by sodium. Transport of conjugated bil e acids was trans-stimulated by bicarbonate in the jejunum. Absorption of c onjugated dihydroxy-bile acids was almost twice as fast as of trihydroxy-bi le acids. Coincubation with other conjugated bile acids, bromosulfophthalei n, and DIDS, as well as by incubation in the cold inhibited the transport r ate effectively. Absorption of conjugated bile acids in the jejunum from th e rat is driven by anion exchange and is most likely an antiport transport.