Aggregate formation is promoted by increasing platelet density. Washed platelets (150 × 106/mL) reconstituted with RBCs were perfused through microcapillary tubes coated with VWF (10 μg/mL) and fibrinogen (50 μg/mL) at 1800 s−1. The platelet count was adjusted to 5 × 106/mL, 20 × 106/mL, 50 × 106/mL, 150 × 106/mL, 400 × 106/mL, or 800 × 106/mL. (A) Unstable and stable aggregate formation was quantified by determining the number of aggregates within a 70 × 90 μm visual field over a 240-second period. An aggregate composed primarily of reversibly adherent platelets was classified as “unstable,” while a “stable” aggregate was classified as one composed of irreversibly adherent platelets. (B) Total amount of platelets recruited into stable aggregates. Each point represents the mean ± SEM from 3 independent experiments. *ND, quantitation was not performed because multiple small aggregates merge together into larger single aggregates. (C) Data from panel A were used to determine the time for the initial nucleating platelet to adhere to the VWF/fibrinogen matrix. Data shown are representative of 5 independent experiments.
