Focal adhesions and actin cables in fibrinogen-adherent platelets. Washed platelets were incubated for 4 hours at 37°C in the absence (A through E) or presence (F through J) of 400 μg/mL C3 exoenzyme. They were then diluted in incubation buffer and placed over fibrinogen-coated coverslips for 60 minutes at 37°C in the presence of 100 nmol/L PMA to enhance spreading. Vinculin was stained with a specific monoclonal antibody and FITC antimouse IgG and F-actin was stained with rhodamine phalloidin. Single views of individual spread platelets were obtained by confocal microscopy. The five platelet pairs shown (eg, A and F, B and G, etc) are from five separate platelet donors and are representative of predominant morphologies. Arrows point to some of the green-staining focal adhesions, which were scored positive on the basis of heavy focal vinculin staining, as reported previously.27 Arrowheads point to some of the red-staining actin cables often seen to connect the focal adhesions. Note that focal adhesions and actin cables were prominent in control platelets, but not in platelets treated with C3 exoenzyme. Bar = 5 μm.