Surface topology and cytoskeleton of activated mouse platelets.

Mouse platelets were examined for shape change by electron microscopy. WT (A) and SLP-76–deficient (B, C) platelets were activated on a CRP-coated coverslip surface, as in Figure 2. WT (D) and SLP-76–deficient (E, F) platelets were attached to coverslips and activated with 1 U/mL thrombin. Cells were either fixed (A, B, D, E) or permeabilized with Triton X-100 in PHEM buffer (C, F), rapidly frozen, freeze-dried, and metal-coated. SLP-76–deficient platelets exposed to CRP retain their disc shapes, though they grow a small number of short filopodia. The cytoskeleton is similar to that of the normal resting mouse platelet cytoskeleton. SLP-76–deficient platelets activated with thrombin spread normally on the surface. The cytoskeleton has rearranged from the resting form and has a cortex composed of short filaments in an orthogonal network.