Surface-exposed actin binds plasminogen on the membrane of agonist-activated platelets: a flow cytometry study

Abstract

Aim.To elucidate whether actin exposed on the surface of agonist-activated platelets is re-sponsible for plasminogen binding. Methods. Human washed platelets were obtained by gel-filtration on Sepharose-2B. The levels of exposed actin on the outer surface of plasma membrane of intact and thrombin- or collagen-stimulated platelets were monitored by flow cytometry. The binding of plasminogen fluorescent conjugate (Pg-FITC) with platelets treated with anti-actin antibody or non-immune IgG (control) was analyzed cytometrically. Results. Thrombin or collagen exposure resulted in the dose-dependent actin expression on the surface of stimulated platelets. Pre-treatment of stimulated platelets with specific anti-actin antibodies was shown to significantly prevent the binding of Pg-FITC with the platelet surface. Conclusion. The results of the present study indicate that actin exposed on the platelet surface at the agonist-induced activation is involved in the plasminogen binding.