Intestinal transport of taurocholate in the cat.

In the present study, the transport of taurocholate by brush border membrane vesicles (BBMV), prepared from the proximal and distal half of the small intestine of cats was investigated. Uptake of taurocholate (0.01 mmol/l) into BBMV from the distal small intestine was clearly enhanced in the presence of an inwardly directed initial Na+ gradient compared to choline+ gradient conditions, whereas uptake by BBMV from the proximal half of the small intestine was not substantially different between the two incubation conditions. Calculated uptake of taurocholate at a 10s incubation period was mainly due to transfer of taurocholate into the vesicular lumen rather than to extensive binding of taurocholate to the membranes. Evaluation of the kinetics of taurocholate transport across the brush border membrane of the distal half of the small intestine under Na+ gradient conditions revealed a saturable Na(+)-dependent component and a diffusive component with the subsequent apparent parameters: Vmax (maximal transport velocity) = 0.59 nmol/mg protein.10s, KM (affinity constant) = 0.12 mmol/l, D (diffusion constant) = 2.0 microliters/mg protein.10s. The results indicate Na+/taurocholate co-transport across the brush border membrane of the distal half of the small intestine in cats. Thus, the carrier-mediated intestinal bile salt absorption in the cat appears to be similar as described in other species.