Inhibition of bile salt transport in brush-border membrane vesicles from rat small intestine by photoaffinity labeling.

The uptake of photolabile bile acid derivative, (7,7-azo-3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24 oyl)-2-aminoethanesulfonate (7,7-azo-TC), was investigated in rat ileal brush-border membrane vesicles. The uptake of 7,7-azo-TC showed a transient vesicle to medium ratio greater than one in the presence of a Na+ gradient. The Na+-dependent uptake of 7,7-azo-TC was inhibited by taurocholate and vice versa. 130 microM 7,7-azo-TC inhibited Na+-dependent taurocholate uptake by 50%. The degree of inhibitory power on taurocholate uptake was taurodeoxycholate greater than cholate greater than 7,7-azo-TC. Photoaffinity labeling of membrane vesicles with 7,7-azo-TC irreversibly inhibited Na+-dependent taurocholate and D-glucose transport but not Na+-dependent L-alanine transport. Kinetic and photoaffinity labeling experiments indicate that this representative photoaffinity probe interacts with the ileal Na+, bile salt cotransporter and may be used to identify polypeptide components of this transport system.