title: Studies on platelets of patients with inherited platelet disorders suggest that collagen-induced fibrinogen binding to membrane receptors requires secreted ADP but not released alpha-granule proteins.
abstract: Collagen induces a saturable 125I-fibrinogen binding to normal human platelets. A role for secreted ADP in this process is supported by studies on 2 patients with the Chédiak-Higashi syndrome. Both collagen-induced nucleotide release and 125I-fibrinogen binding were strongly reduced while ADP-induced fibrinogen binding was normal. Platelets from 2 patients with the gray platelet syndrome bound normal amounts of 125I-fibrinogen in the presence of ADP or collagen despite the severe reduction of secretable alpha-granule proteins. Binding did not occur to collagen-stimulated type I thrombasthenic platelets which lacked GPIIb-IIIa complexes but was detected in amounts which correlated with the residual concentrations of GPIIb-IIIa in the platelets of a patient with type II disease. Our results allow us to propose that collagen-induced fibrinogen binding to normal platelets requires the presence of GPIIb-IIIa complexes and secreted ADP but proceeds independently of alpha-granule release.
mesh_terms: D000244:Adenosine Diphosphate / Q000097:blood*; D000255:Adenosine Triphosphate / Q000378:metabolism; D001778:Blood Coagulation Disorders / Q000097:blood*; D001792:Blood Platelets / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D002609:Chediak-Higashi Syndrome / Q000097:blood; D003094:Collagen / Q000097:blood*; D003594:Cytoplasmic Granules / Q000378:metabolism; D005340:Fibrinogen / Q000097:blood*; D006023:Glycoproteins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D008565:Membrane Proteins; D010980:Platelet Membrane Glycoproteins; D011956:Receptors, Cell Surface; D012701:Serotonin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005340:Fibrinogen; D003094:Collagen