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

Abstract

The uptake of taurocholate was studied in membrane vesicles isolated from brush borders of hamster jejunum and ileum. When an extra- to intra-vesicular gradient of Na+ ions was present ileal vesicles took up 10 times more taurocholate than did jejunal vesicles. Accumulation of taurocholate by ileal vesicles was transient and was due to transport of this bile salt into an osmotically active intravesicular space rather than simple binding. Uptake of taurocholate was specifically dependent on Na+ ions; NaCl and Na2SO4 were capable of supporting accumulation, whereas KCl, LiCl and mannitol were not. Na+-coupled uptake of taurocholate into ileal vesicles was inhibited by other trihydroxy bile salts, by preloading the vesicles with Na+ and by simultaneous flow of glucose into the vesicles. Similarly, vesicular uptake of glucose was inhibited by simultaneous uptake of taurocholate. These results demonstrated that brush-border membrane vesicles prepared from ileum possess an Na+-coupled co-transport system for taurocholate that is similar to the active bile-salt transport system present in the intact ileum.