Pharmacological inhibition or siRNA-mediated knockdown of Rac1 impaired baseline endothelial barrier integrity.

<p><i>A</i>. Treatment with the selective Rac1 inhibitor Z62954982 reduces TER in a concentration-dependent manner in HDMEC monolayers. <i>B</i>. Comparison of the mean maximum decreases in TER in the 30-min time window for each concentration of Z62954982 in HDMEC monolayers. Panels <i>C & D</i> show that Z62954982 produces a similar concentration-dependent TER in HUVEC monolayers. <i>E</i>. Western blot confirming knockdown (KD) with Rac1-specific siRNA, compared to sham and scrambled RNA (Scr) control groups. Bands for β-actin from re-probed blots confirmed equivalent loading of protein for each lane. <i>F</i>. Mean baseline TER values of HDMEC and HUVEC monolayers in Rac1 knockdown, scrambled control, and sham-transfected groups. *P<0.05 versus vehicle treated group. †P<0.05 versus other concentrations.