Thrombin binding to platelets and their activation in plasma Journal Articles uri icon

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abstract

  • Summary. The interactions of α‐thrombin with platelets are critical in haemostasis and arterial thrombosis. This study established methods for characterizing the binding of α‐thrombin to platelets and some of its consequences in platelet‐rich plasma. The binding of α‐thrombin to platelets and the subsequent platelet activation were quantified by flow cytometry, using affinity purified polyclonal antibodies to human α‐thrombin and a monoclonal antibody to GMP‐140, respectively. Dose‐dependent binding of α‐thrombin to platelets and their activation occurred in parallel, both reaching the maxima for each enzyme concentration within 10 s after → 1.0 nmα‐thrombin was added to recalcified PRP containing 1 μm recombinant tick anticoagulant peptide. The tick anticoagulant peptide abrogated prothrombin activation in the platelet‐rich plasma. α‐Thrombin binding to platelets, and their activation, were abrogated by a monoclonal antibody to the hirudin tail‐like domain of the seven transmembrane thrombin receptor on platelets. Therefore this receptor represents an important site for α‐thrombin binding to platelets suspended in plasma. d‐Phe‐Pro‐ArgCH2‐α‐thrombin only bound to platelets when its concentration was → 100 nm, and it did so without inhibiting platelet activation by α‐thrombin. Whereas concentrations of hirudin equimolar to those of α‐thrombin failed to abrogate α‐thrombin‐mediated activation of platelets, a 10‐fold molar excesses of hirudin over α‐thrombin abrogated α‐thrombin binding to platelets. The demonstration that → 1.0 nmα‐thrombin can bind to platelets and initiate their activation raises the possibility that the levels of thrombin generated in venous and arterial thrombosis contribute to platelet activation in vivo.

authors

publication date

  • November 1994