Spreading but not adhesion of mouse platelets on laminin is dependent on GPVI. (A) Washed murine platelets (3 × 10⁷/mL) from control or GPVI-deficient mice (GPVI^-/-) were pretreated with or without 1 mM GRGDS peptide in the presence or absence of 20 μg/mL anti–integrin α₆ antibody. Laminin-coated coverslips were prepared as described in Figure 1. Platelets were seeded on laminin-coated coverslips for 30 minutes at room temperature. Adherent platelets were fixed, permeabilized, stained, and photographed using fluorescent microscopy as described in Figure 1. (B) The number of adherent platelets (i) and total surface coverage of adherent platelets on laminin (ii) were from at least 10 different images from 2 separate experiments.