Characterisation of the binding of apolipoprotein E-free high density lipoprotein to cultured human endothelial cells

125I]-labelled apolipoprotein E-free high density lipoprotein (apo E-free HDL) binds to cultured human endothelial cells with high affinity. Competitive binding experiments showed that complexes of egg phosphatidyl choline with respectively apo A-1, A-2 and E, and phosphatidyl choline vesicles alone, competed efficiently with 125I]-apo E-free HDL for binding, suggesting that the binding of HDL to the high affinity receptor is not mediated by recognition of one specific apolipoprotein. Analyses of the respective incubation media of the competitive binding experiments by density gradient ultracentrifugation showed that the 125I]-label of 125I]-HDL redistributes to the competitors used. This implies that the usual competitive binding experiments may not be used in order to investigate which HDL component is involved in the high affinity binding of HDL to the plasma membrane.