Characterization of bile acid binding to rat intestinal brush border membranes

Abstract

Studies were performed to characterize the binding1 of bile acids to intestinal brush border membranes. Total 14C-taurodeoxycholate binding was: 1) similar for brush borders prepared from jejunum and ileum, 2) linear with respect to monomer concentration, 3) uninhibited by a structural analog, and 4) not depressed by boiling or trypsin. A linear relationship existed between binding and the number of hydrogen bonds formed by a bile acid and the slope of the line corresponded to delta deltaF of 300 cal/mol. The binding of bile acids to the 105,000 x g supernatant fraction of sonicated brush borders was similar to the binding of phospholipid liposomes using gel chromatography. These data suggest that: 1) the kinetics and characteristics of binding of bile acid to ileal brush borders do not reflect the kinetics and characteristics of active ileal transport previously obtained in whole tissue preparations, but instead reflect the kinetics and characteristics of passive jejunal transport; 2) a determinant of binding is hydrogen bonding with water; 3) isolated intact brush borders are relatively polar membranes; and 4) binding to solubilized brush borders may represent partitioning between the aqueous phase and membrane lipid.

Taurocholate transport by rat intestinal basolateral membrane vesicles. Evidence for the presence of an anion exchange transport system.

“…A characteristic ofthis transporter is that it can be driven additionally by a transmembrane pH difference (15). Studies to determine the influence ofa proton gradient on bile acid uptake are subject to artifact because the binding of bile acid to membrane surfaces is sensitive to changes in pH (27). For these reasons, sulfate was chosen as a test anion to determine whether the anion exchange transporter in intestinal basolateral membrane vesicles is sensitive to a transmembrane pH difference and is shared by taurocholate.…”

Sodium ion-coupled uptake of taurocholate by intestinal brush-border membrane vesicles

“…Several laboratories have utilized membranes isolated from intestinal epithelial cells to investigate the mechanisms responsible for intestinal absorption of bile salts. Wilson & Treanor (1977) isolated brushborder membranes from rat intestine and examined uptake of several bile salts by this preparation. Although the membranes did take up bile salts, the characteristics of uptake by the brush-border membranes were quite different from those for intestinal absorption.…”

Sodium-coupled Taurocholate Transport in the Proximal Convolution of the Rat Kidney In Vivo and In Vitro

“…An inside Na+ gradient. However, at 60 min (equilibrium) tauroated across the cholate uptake was higher under conditions of lowest g vesicles with pH on both sides ofthe vesicle membrane (pHo 6/pHi 6) a K+ medium as which may represent greater partitioning of bile acid periments were into the vesicle membrane (21). e of a Na+ gradiSubstrate specificity.…”