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.
Vickers
J D
JD
Department of Pathology, Faculty of Health Sciences, McMaster University, Hamilton, Canada.
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