Thromb Haemost 1993; 69(02): 124-129
DOI: 10.1055/s-0038-1651567
Original Article
Coagulation
Schattauer GmbH Stuttgart

Plasma Factor V Activation Is Prevented by Activated Protein C in the Presence of Phospholipid Vesicles, Not Platelets

Susan Solymoss
The St. Mary’s Hospital Centre, McGill University, Montreal, Canada
,
Kim Thi Phu Nguyen
The St. Mary’s Hospital Centre, McGill University, Montreal, Canada
› Author Affiliations
Further Information

Publication History

Received 04 March 1992

Accepted after revision 07 October 1992

Publication Date:
03 July 2018 (online)

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Summary

Activated protein C (APC) is a vitamin K dependent anticoagulant which catalyzes the inactivation of factor Va and VIIIa, in a reaction modulated by phospholipid membrane surface, or blood platelets. APC prevents thrombin generation at a much lower concentration when added to recalcified plasma and phospholipid vesicles, than recalcified plasma and platelets. This observation was attributed to a platelet associated APC inhibitor. We have performed serial thrombin, factor V one stage and two stage assays and Western blotting of dilute recalcified plasma containing either phospholipid vesicles or platelets and APC. More thrombin was formed at a given APC concentration with platelets than phospholipid. One stage factor V values increased to higher levels with platelets and APC than phospholipid and APC. Two stage factor V values decreased substantially with platelets and 5 nM APC but remained unchanged with phospholipid and 5 nM APC. Western blotting of plasma factor V confirmed factor V activation in the presence of platelets and APC, but lack of factor V activation with phospholipid and APC. Inclusion of platelets or platelet membrane with phospholipid enhanced rather than inhibited APC catalyzed plasma factor V inactivation. Platelet activation further enhanced factor V activation and inactivation at any given APC concentration.

Plasma thrombin generation in the presence of platelets and APC is related to ongoing factor V activation. No inhibition of APC inactivation of FVa occurs in the presence of platelets.