Spreading of human platelets on laminin is mediated through GPVI. (A) Coverslips were coated with 50 μg/mL laminin or 50 μg/mL collagen and blocked with 2% BSA. Washed human platelets (2 × 10⁷/mL) were pretreated with PBS (i), 100 μg/mL GPVIex (ii), or 100 μg/mL GPVI-Fc₂ (iii) in the presence of 1 mM GRGDS. Platelets were seeded on BSA-, laminin- or collagen-coated coverslips for 30 minutes at room temperature. Unbound platelets were removed, and adhered platelets were fixed, stained, and visualized as described in Figure 1. (B) (i) The number of adherent platelets was counted. The graph illustrates the mean number of adherent platelets ± SEM per 0.006 mm² from at least 8 different images in 1 experiment, which is representative of 2 separate experiments. (ii) Total surface coverage of adherent platelets on laminin- or collagen-coated surfaces was measured. The graph illustrates the percent control surface coverage ± SEM per 0.006 mm² from at least 8 different images in 1 experiment, which is representative of 2 experiments. (C) Different concentrations of GPVI-Fc₂ were flowed over an immobilized laminin (i), collagen (ii), or a control surface. The arrows indicate the beginning and end of perfusion of GPVI-Fc_2. The results are shown from 1 experiment that is representative of 4 others. RU indicates resonance units.