The binding of high density lipoproteins to isolated rat hepatocytes

Abstract

The association of ¹²⁵I-labelled rat high density lipoproteins (¹²⁵I-HDL) to suspended rat hepatocytes was studied at 4°C. ¹²⁵I-HDL associated to isolated hepatocytes by two processes—one of high and one of low affinity. The cell-association of ¹²⁵1-HDL exhibited saturation kinetics and was inhibited to varying degrees with both rat and human lipoproteins such as VLDL, LDL and HDL but not by lipoprotein deficient serum or asialo-fetuin. The cell-association of ¹²⁵1-HDL did not require divalent cations and could be reduced by pronase treatment of the cells. The binding site was clearly different from the receptor for LDL in extrahepatic cells since heparin and apolipoprotein E did not compete for the HDL binding. Concanavalin A reduced cell-association of both protein and cholesterol ester labelled HDL. The number of binding sites for HDL at 4°Cwas 2.2 × 10⁶ per cell and the association constant (K_a) 8.2 × 10⁶ (mol/1) ⁻¹ Experiments with HDL labelled with [³H] cholesterol by means of lecithin: cholesterol acyltransferase (LCAT, EC 2.3.1.43) in the cholesterol ester moiety suggested that the same mechanism was responsible for the cell-association of HDL prepared this way.

Key Words:

• cell binding
• hepatocytes
• high density lipoproteins
• lipoprotein metabolism
• low density lipoproteins
• rat liver