Kinetics of taurocholate uptake by the perfused rat liver

The uptake of taurocholate (TC) by the perfused rat liver was studied by the multiple indicator dilution technique using single injections of 14-C-labeled TC and 99m-Tc-labeled albumin. For determination of the intra- and extravascular space, 51-Cr-labeled erythrocytes and albumin were used. TC was found to be distributed into an extravascular space equivalent to that of albumin. Analysis of the dilution curves, according to Goresky (Am J Physiol 207:13-26, 1964), revealed that the initial TC uptake rate increased with increasingly TC dose in a nonlinear fashion, exhibiting saturation kinetics which obeyed the Michaelis-Menten equation. The initial maximal uptake rats (Vmax) was found to be 32.5 nmoles per s and g of liver, a value exceeding the maximal steady state capacity (Tm) for excretion of TC into the bile. The half-saturation constant (Km) was 90.6 nmoles per g of liver, indicating that this system is operating far from saturation at physiological levels of bile acids in portal blood.