Uptake of Taurocholic Acid into Isolated Rat‐Liver Cells

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Abstract
Binding and transport characteristics for uptake of taurocholic acid by isolated rat liver cells were studied. 1 An adsorption of taurocholate to the cell surface is terminated in less than 15 s. A Ks of 0.55 mM and a total binding capacity of 3.8 nmol/mg cell protein is determined. 2 The rate of uptake of taurocholate follows Michaelis-Menten kinetics with Km= 19 μM and V= 1.7 nmol/mg protein min. 3 There is a broad pH optimum for uptake between pH 6.5–8.0. 4 The activation energy amounts to 29 kcal/mol. At high taurocholate concentration an unusual upward bend is observed in the Arrhenius plot. 5 Taurocholate uptake is competitively inhibited by taurochenodeoxycholate (Ki= 9 μM). It is noncompetitively inhibited by bromosulfophthalein (Ki= 3 μM). 6 At physiological taurocholate concentrations a 200-fold intracellular accumulation of taurocholate is observed. 7 Uptake is inhibited by about 75% by either antimycin A, carbonylcyanide m-chlorophenyl-hydrazone, ouabain. 8 Replacement of extracellular Na+ by either K+ or sucrose results in a 75% decrease of uptake. 9 It is concluded that taurocholate uptake is a carrier-mediated process, and suggested that the energy for intracellular accumulation is made available by cotransport of Na+.