An essential role for vWf, GPIb/V/IX, and integrin α_IIbβ₃ in mediating shear-induced platelet aggregation in the presence or absence of cytochalasin D.

(A) Platelet-rich plasma (PRP) from an individual with type III vWD was incubated with either vehicle alone (−CD, i) or 5 μmol/L CD (+CD, ii) prior to exposing platelets to a shear rate of 5000 s⁻¹ (top panel). Alternatively, purified HvWf (20 μg/mL) was added to vWD PRP (+ vWf) prior to their exposure to the indicated shear rates. The size of platelet aggregates formed under the various experimental conditions was determined as described in Figure6. (B) Washed platelets from a normal donor were incubated with an anti-GPIb (ALMA12) or anti-β₃ integrin mAb (c7E3 Fab) for 10 minutes in the presence of 5 μmol/L CD (+ CD) prior to the exposure of platelets to shear (5000 s⁻¹). Platelets were then imaged as described in Figure 6. (C) Platelet aggregates from 8 random fields (10 × objective) were subjected to volumetric analysis, and the extent of aggregation was expressed as the fold increase in the volume of aggregates over that detected for Me₂SO-treated control platelets. Results for vWD platelets are from a single vWD patient and results for normal platelets are the mean ± SE from 5 experiments. ░, buffer; ▪, 5 μmol/L.