ADP-stimulated fibrinogen binding is necessary for some of the inositol phospholipid changes found in ADP-stimulated platelets.
ADP-stimulation of washed human platelets suspended in Tyrode/albumin solution containing Ca2+ (2 mM) and fibrinogen (0.4 mg/ml) causes extensive, reversible aggregation without appreciable secretion of granule contents. Under these conditions ADP (10 microM) stimulation decreased the amounts of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) and phosphatidylinositol 4-phosphate (PtdInsP) at 10 s. Omitting fibrinogen from the suspending medium or blocking fibrinogen binding to the platelets using Arg-Gly-Asp-Ser (RGDS, 0.23 mM) inhibited these decreases in PtdInsP2 and PtdInsP. In contrast, ADP-induced decreases in PtdInsP2 and increases in PtdInsP at 60 s compared to 10 s were not affected by RGDS or the absence of fibrinogen. In platelets prelabelled with [3H]glycerol and [32P]phosphate, changes in labelling of the inositol phospholipids paralleled the changes in amount. The ADP-induced changes in phosphatidic acid (PtdOH) at 10 s were unaffected by RGDS; this finding supported previous reports that phospholipase C was not the cause of the early decreases in PtdInsP2 and PtdInsP. These results indicate that the early decreases in PtdInsP2 and PtdInsP at 10 s are dependent on fibrinogen binding to the platelets and occur after fibrinogen binding which is activated by ADP stimulation. It is proposed that the fibrinogen-dependent changes in PtdInsP2 and PtdInsP may have a feedback role augmenting platelet aggregation or other responses of platelets that might occur after fibrinogen binding, possibly due to effects on actin polymerisation.
Department of Pathology, Faculty of Health Sciences, McMaster University, Hamilton, Canada.
J D
JD
Vickers
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D009842:Oligopeptides / Q000494:pharmacology; D010712:Phosphatidic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology
D009842:Oligopeptides; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D010975:Platelet Aggregation Inhibitors; D000244:Adenosine Diphosphate; D005340:Fibrinogen; C046617:arginyl-glycyl-aspartyl-serine