Inhibition of integrin activation in Rap1b-deficient ECs. Adhesion of calcein-AM-labeled WT and Rap1b^−/− ECs to vitronectin- (A-B) or fibronectin- (C-D) coated 96-well plates in the absence or presence of β₃-blocking antibody was measured using fluorescent plate reader. (E-G) Adhesion of integrin β₃^−/− ECs to fibronectin in the absence or presence of Rap1b siRNA. Efficiency of Rap1b knockdown and integrin β₃ knockout was confirmed by Western blot with P₃-specific and Rap1-specific antibodies (E). Panels B, D, and G are normalization of data in panels A, C, and F, respectively. Graphs represent mean value of mutant EC adhesion value relative to that of control ECs obtained in 4 independent experiments performed in triplicate. Error bars represent SEM. P values were obtained using paired t test.