GLYCOPROTEINS IIB IIIA INVOLVED IN THE ACTIVATION OF HUMAN PLATELETS BY LOW-DENSITY LIPOPROTEINS/

Low density lipoproteins (LDL) enhance the entry of Ca2+ and other div alent cations into platelets via receptor-driven channels. The use of a synthetic peptide and of antibodies blocking the interaction of glyc oproteins IIb and IIIa with their ligands demonstrated that these fibr inogen receptor antagonists impede LDL-induced platelet aggregation wi thout affecting the ability of LDL to increase the cytoplasmic level o f Ca2+. Based on these findings, it is concluded that the complex of g lycoproteins IIb and IIIa is not involved in LDL-induced activation of secondary messenger systems but plays an aggregation-promoting role b y providing cell-to-cell interactions.