[Amplification and inhibition of platelet function by serum lipoproteins]

Low-density lipoprotein (LDL) at a concentration of 100 micrograms/mL, which is near the dissociation constant (Kd) of LDL-binding, had a maximal stimulatory effect on agonist-induced platelet aggregation. Anti-LDL receptor monoclonal antibody (C-7), like native LDL, induces a transient increase in intracellular Ca2+ and a shape change of human platelets. On the other hand, high-density lipoprotein (HDL) inhibited platelet function. ApoE-rich HDL, as well as, apoE.DMPC potently inhibited platelet aggregation in a dose-dependent manner. ApoE.DMPC stimulated the release of cholesterol into the supernatant, suggesting that apoE plays a major role in the inhibitory effect of apoE-rich HDL in platelet function, presumably due to the release of cholesterol from the plasma membrane.