ROLE OF PLATELET FACTOR XA IN CHYLOMICRON-PROTHROMBIN COMPLEXES INDUCED PLATELET ACTIVATION

The effects of chylomicron-prothrombin complexes on platelet activation, including platelet aggregation, serotonin release, arachidonic acid release and increases of platelet cytosolic [Ca2+](i) were examined. Furthermore the role of platelet factor Xa on the conversion of chylomicron bound prothrombin to thrombin was studied by using a synthetic inhibitor of factor Xa, TenStop. The chylomicron-prothrombin complexes could induce platelet aggregation and enhance the platelet serotonin release and arachidonic acid release in contrast to native chyle chylomicrons. An increase of platelet [Ca2+](i) was observed during incubation with chylomicron-prothrombin complexes. TenStop inhibited platelet aggregation and serotonin release that were induced by chylomicron-prothrombin complexes in a dose-dependent manner, whereas the TenStop itself did not inhibit the platelet aggregation induced by thrombin and collagen. It is concluded that platelet activation induced by chylomicron-prothrombin complexes is related to the platelet factor Xa that could be the key factor in the conversion of chylomicron bound prothrombin to thrombin. (C) 1995 Academic Press, Inc.