Preincubation accelerates taurocholate uptake into isolated liver cells

The effect of 3-sulphation and taurine conjugation on the uptake of chenodeoxycholic acid by rat hepatocytes

The hepatic uptake of chenodeoxycholic acid, taurochenodeoxycholic acid, chenodeoxycholic acid 3-sulphate and taurochenodeoxycholate acid 3-sulphate by isolated rat hepatocytes was examined. Taurochenodeoxycholic acid, taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate uptake occurred by a saturable, energy-dependent process while chenodeoxycholic acid uptake was predominantly non-saturable, possibly simple diffusion. Apparent Km (mumol/l) and Vmax (nmol/mg protein per min) values (mean +/- S.D.), respectively, were: chenodeoxycholic acid (saturable component), 33 +/- 6.4 and 4.8 +/- 0.6; taurochenodeoxycholic acid, 11.1 +/- 2.0 and 3.1 +/- 0.5; chenodeoxycholic acid 3-sulphate, 6.1 +/- 0.9 and 2.3 +/- 0.4; and taurochenodeoxycholic acid 3-sulphate, 5.0 +/- 0.7 and 0.9 +/- 0.15. Both conjugation with taurine and sulphation at the 3 position resulted in a reduction in the values of Km and Vmax. Uptake of each of the bile acids taurochenodeoxycholic acid, taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate was competitively inhibited by the other two, with taurochenodeoxycholic acid a potent inhibitor of both taurochenodeoxycholic acid 3-sulphate and chenodeoxycholic acid 3-sulphate uptake. Other bile acids also inhibited. Uptake was inhibited by albumin in the order chenodeoxycholic acid 3-sulphate greater than taurochenodeoxycholic acid 3-sulphate greater than taurochenodeoxycholic acid and was dependent on the extent of bile acid binding to albumin.

Kinetics of taurocholate uptake by isolated ileal cells of guinea pig

Carrier-mediated uptake of taurocholate by ileal cells of guinea pig had an activation energy of 66 kJ/mol. There was no distinct pH optimum in the physiological pH range. Uptake was efficiently inhibited by cholate and taurochenodeoxycholate in a competitive manner, but less inhibited by bromosulfophthalein and not inhibited by taurine. The rate of uptake was related to the extracellular Na+ concentration up to 90 mM Na+. Stimulation by Na+ (up to sevenfold) occurred only in the presence of a transmembrane Na+ gradient, whereas high extracellular (Na+) in the absence of gradient did not stimulate. It is suggested that taurocholate is bound to a steroid-binding site of the carrier. The energy for the intracellular accumulation is largely provided by cotransport with Na+.

Bile acid uptake by isolated intestinal mucosa cells of guinea pig

Isolated intestinal mucosa cells of the guinea pig were employed to study intestinal transport of bile acids. Chenodeoxycholate and lithocholate were rapidly taken up into jejunal and ileal cells by diffusion. Taurocholate and cholate however showed only a minor diffusion rate and were preferentially taken up by the ileal bile acid carrier. This uptake was saturable with an apparent Km of 231 microM and V of 7 nmol/mg protein per min for taurocholate; this bile acid was accumulated 90-fold. Its uptake was strongly inhibited by antimycin A, FCCP, ouabain or Na+ -deficiency in the medium. Sugars or amino acids did not interfere with uptake. Experimental conditions were optimized with regard to incubation medium, cell amount, cell age and length of preincubation. It is concluded that ileal cells of the guinea pig are superior to other experimental models for characterizing the ileal bile acid carrier, because they allow us to determine initial rates of uptake and have a very efficient energetic coupling.