Localization of filamin, GPIb and actin in spreading platelets. Platelets spread on a VWF matrix were fixed, permeabilized, and costained with filamin antibodies and phalloidin (Ai-ii), GPIbα antibodies and phalloidin (B), GPIbα and filamin antibodies (C), vinculin antibodies (D), and cortactin antibodies (D). Arrows in merged images in (5Aii) indicate colocalization of filamin and submembraneous actin at lamellipodia. Cells were visualized by confocal microscopy. Bars, 10 μm.