| Abstract: | The aim of this study was to determine the kinetic parameters of the hepatic uptake of VLDL remnant cholesteryl esters. Rat livers were perfused in situ with a broad range of remnant 3H]cholesteryl ester concentrations of known specific radioactivity. Following exactly 3 min of perfusion, hepatic lipids were extracted and labelled cholesteryl esters were separated by thin-layer chromatography and counted. The rate of cholesteryl ester uptake was a saturable process and the apparent kinetic parameters were determined from the Lineweaver-Burk plot of the data. Km and Vmax were calculated to be 72 microM and 35 nmol cholesteryl ester/min per g liver, respectively. For the purpose of comparison, we have expressed our kinetic parameters in terms of number of particles (Vmax = 0.022 nmol particles/min per g liver and Km = 45 nM) and compared our values with those obtained with chylomicron remnants by another group of investigators (Sherrill, B.C., Innerarity, T.L. and Mahley, R.W. (1980) J. Biol. Chem. 255, 1804-1807). We found that the maximal capacity for the removal of VLDL particles was similar to what was observed with rat chylomicron remnants. In contrast, the Km for the uptake process of VLDL remnant particles was approximately four times higher than that of rat chylomicron remnant particles. Our results are consistent with the hypothesis that hepatic removal of both chylomicron and VLDL remnants is mediated by the same receptor, but suggest that the affinity of VLDL remnants for the hepatic removal process is substantially lower, possibly due to structural differences between the two remnant particles. |
