ABSTRACT
Incubation of rat hepatic sinusoidal cells with FITC-HDL(2), FITC-ox-HDL(2) and [(3)H]CE-HDL(2)(rHDL(2)), ox-rHDL(2) showed that binding of FITC-HDL(2) to the cells was competitive to ox-HDL(2), but not to HDL(2). The cell-endocytic fluorescence strength (FS) of FITC-HDL(2) and radioactivity of ox-rHDL(2) were 45.5% of that of FITC-HDL(2) and 61.4% of that of rHDL(2), respectively. Endocytic FS and radioactivity were mainly in TCA-precipitable and supernatant part, respectively. The cell-released FS and radioactivity were 67.7% and 10.9% of the cell-endocytic FS and the radioactivity, respectively, and both of them were mainly TCA-precipitable. These results suggest that: (1) There is probably an ox-HDL receptor on the surface of rat hepatic sinusoidal cells, which is different from HDL receptor. (2) The metabolic behaviour of ox-rHDL(2) in the cells is similar to HDL(2). Both of them do not take a lysosomal pathway. Apoproteins and CE components dissociate from endocytic lipoprotein in the cells. After the cells have taken up most of CE, the residual CE recombines with apolipoprotein to form a lipoprotein and is released from the cells by retroendocytosis. (3) Oxidative modification of HDL(2) weakens its ability to cholesterol reverse transport.
ABSTRACT
The recombined (3)H-CE-HDL(2)(rHDL(2)) keeps the biological activities of the native HDL(2). After rat hepatic sinusoidal cells were incubated with rHDL(2) at 37 degrees for 3 h (normal group), the cell-endocytic cpm was 995-/+147(mean-/+s, n=2). After the cells were further incubated for 2 h, the cell-release TCA-precipitable cpm and the TCA-supernatant cpm were 78-/+32 and 12-/+9 respectively. These values were 339-/+62, 19-/+11 and 9-/+5 respectively in the acetylimidazole-modified group, and 542-/+78, 34-/+14 and 9-/+8 respectively in the heparin-pretreated group. Our results suggested that: (1) Rat hepatic sinusoidal cells internalize HDL(2) and take up HDL(2)-CE by its HDL receptor, and HDL(3) was secreted out of the cells by retroendocytosis. (2) Hepatic lipase (HL) induces directly the selective uptake of HDL(2)-CE by the cells. (3) There is cooperation between the HDL receptor and HL in the selective uptake of HDL(2)-CE by the cells.