Spreading but not adhesion of mouse platelets on laminin is dependent on FcR γ chain. (A) Washed murine platelets (3 × 10⁷/mL) from control or FcR γ chain–deficient mice (FcR γ chain^-/-) were pretreated with or without 1 mM GRGDS peptide. Coverslips were coated with 50 μg/mL laminin and blocked with fatty acid–free BSA as described in Figure 1. BSA-coated coverslips were used for negative control. GRGDS-treated platelets were seeded on BSA- or laminin-coated coverslips for 30 minutes at room temperature. After unbound platelets were removed, platelets were fixed, stained, and photographed 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 from 3 separate experiments. (ii) Total surface coverage of adherent platelets on laminin-coated surfaces was measured. The graph illustrates the percent wild-type surface coverage ± SEM per 0.006 mm² from at least 8 different images from 3 separate experiments. ^**P < .01.