Platelet surface P-selectin molecules increased after exposing platelet toa high shear flow

Background. P-selectin is known to play a crucial role in leucocyte recruit ment at sites of vascular injury. Although platelet surface expression of P -selectin molecules are well known to occur after platelet stimulation by c hemical agonists such as alpha-thrombin, it is still uncertain whether P-se lectin expression occurs in the process of the more physiological platelet activation pathway mediated by interaction between von Willebrand factor (v WF) and platelet receptor proteins, including glycoprotein (GP) Ib alpha an d GP IIb/IIIa, occurring under high shear rates generated by blood flow. Methods. We have developed a method to detect P-selectin molecules expresse d on platelet surface with flow-cytometer and monoclonal antibody, which ca n bind exclusively to P-selectin (WGA1), directly conjugated with fluoresce in isothiocynate. This method allowed us to measure platelet surface P-sele ctin molecules semiquantitatively. Results. We demonstrated that a significant increase in platelet surface P- selectin molecules occur after exposing platelets to a relatively high shea r rate of 10,800 s(-1). We have also demonstrated that shear-induced surfac e expression of P-selectin as well as microparticle release from platelets depended at least on the interaction between von Willebrand factor and glyc oprotein Ib alpha, a platelet surface receptor for the former. Conclusions. Shear-induced von Willebrand-mediated surface expression of P- selectin may play a role in leucocyte recruitment in platelet thrombi at va scular injury sites.