EXPRESSION OF PROTHROMBINASE ACTIVITY AND CD9 ANTIGEN ON THE SURFACE OF SMALL VESICLES FROM STIMULATED HUMAN ENDOTHELIAL-CELLS

We employed flow cytometry and monoclonal antibodies (MoAb) to study t he surface membrane protein of shed particles (small vesicles: SV) tha t were released from vascular endothelial cells (EC) by agonists such as a Ca ionophore (A23187) and thrombin. After stimulation of EC by A2 3187, CD9 antigens disappeared entirely from the EC surface in a time- and concentration-dependent manner; they subsequently moved onto the SV surface. Von Willebrand factor (VWF) and P-selectin from Weibel-Pal ade (W-P) bodies were expressed rapidly on the EC surface after thromb in stimulation: but not on the SV surface. P-selectin may have some ef fect on maintenance of hemostasis on the EC surface. We demonstrated t hat the surfaces of SV and EC significantly supported prothrombinase a ctivity and confirmed that A23187-induced SV from EC express binding s ites for factors IXa and Xa. These results suggest that the SV are an important factor in a novel controlling mechanism of the coagulation s ystem on the EC surface.