The role of LIMK1 in VWF/GPIb-IX–mediated actin polymerization and in platelet spreading. (A) Flow cytometric analysis of the relative amounts of polymerized actin in WT and LIMK1^−/− platelets stimulated with 1 µg/mL botrocetin in the presence or absence of 6.4 µg/mL VWF in an aggregometer at 37°C for 4 and 10 minutes. The ratio between the mean fluorescence intensity values of stimulated platelets versus the baseline phalloidin binding in control platelets is shown. Statistical significance was determined by one-way analysis of variance (*P < .05). (B) Alexafluor-546–labeled phalloidin staining of polymerized actin in WT and LIMK1^−/− platelets spread on VWF (in the presence of 2 µg/mL botrocetin) or fibrinogen-coated coverslides (90 min at 37°C). The scale bars represent 12.5 µm.