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Role of adhesion and contraction in Rac 1-regulated endothelial barrier function in vivo and in vitro

¹Institute of Anatomy and Cell Biology, University of Würzburg, D-97070 Würzburg, Germany; ²Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, California 95616

Submitted 13 November 2003 ; accepted in final form 24 March 2004

We demonstrated previously that inhibition of the small GTPase Rac-1 by Clostridium sordellii lethal toxin (LT) increased the hydraulic conductivity (L_p) of rat venular microvessels and induced gap formation in cultured myocardial endothelial cells (MyEnd). In MyEnd cells, we also demonstrated that both LT and cytochalasin D reduced cellular adhesion of vascular endothelial (VE)-cadherin-coated beads. Here we further evaluate the contribution of actin depolymerization, myosin-based contraction, and VE-cadherin linkage to the actin cytoskeleton to LT-induced permeability. The actin-depolymerizing agent cytochalasin D increased L_p in single rat mesenteric microvessels to the same extent as LT over 80 min. However, whereas the actin-stabilizing agent jasplakinolide blunted the L_p increase due to cytochalasin D by 78%, it had no effect on the LT response. This conforms to the hypothesis that the predominant mechanism whereby Rac-1 stabilizes the endothelial barrier in intact microvessels is separate from actin polymerization and likely at the level of the VE-cadherin linkage to the actin cytoskeleton. In intact vessels, neither inhibition of contraction (butanedione monoxime, an inhibitor of myosin ATPase) nor inhibition of Rho kinase (Y-27632) modified the response to LT, even though both inhibitors lowered resting L_p. In contrast butanedione monoxime and inhibition of myosin light chain kinase completely inhibited LT-induced intercellular gap formation and largely reduced the LT-induced permeability increase in MyEnd monolayers. These results support the hypothesis that the contractile mechanisms that contribute to the formation of large gaps between cultured endothelial cells exposed to inflammatory conditions do not significantly contribute to increased permeability in intact microvessels.

permeability; Rho proteins; actin; stress fibers; vascular endothelial cadherin

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