Effect of RhoA inactivation by C3 exoenzyme on focal adhesion formation in fibrinogen-adherent platelets. Washed platelets were incubated for 4 hours at 37°C with vehicle buffer (“No C3”) or 400 μg/mL of C3. Cells were incubated over fibrinogen-coated coverslips and adherent cells processed for fluorescence microscopy as in Fig 7. Five hundred control and C3-treated platelets were scored as being spread or unspread, the latter defined as rounded and ≤ 5 μm in diameter. Also, 500 spread platelets in each sample were scored for focal adhesions as illustrated in Fig 7. Data represent means ± SEM of four experiments. C3 caused ADP-ribosylation of 64.4% ± 8.0% of the RhoA in this series of experiments.