The Interaction of Factor V with Human Blood Platelets

The coagulant activity of gel filtered human platelets in the factor V assay is low. Lysis of these platelets by repeated freezing and thawing exposes a high coagulant activity, which is due to liberation of the factor V molecule from the damaged cells. Freezing and thawing of gel filtered platelets of a severe factor V deficient patient did not expose any coagulant activity.

Supernatants of centrifugated gel filtered platelet lysates contained specific factor V-antibody neutralizing capacity.

Fluorescence of normal platelets with FITC conjugated with sheep anti-rabbit immunoglobulin was inhibited by previous incubation of rabbit anti factor V-antibody with lysates of gel filtered normal platelets.

It is postulated, based upon these facts that factor V is localized intracellularly.

During collagen-induced aggregation of gel filtered normal platelets, endogenous serotonin is released within ten seconds, in contrast to factor V, which is slowly liberated, parallel with pf-3 activity.