Microtubule disassembly increases endothelial cell barrier dysfunction: role of MLC phosphorylation

Endothelial cell (EC) barrier regulation is critically dependent on cytoske letal components (microfilaments and microtubules). Because several edemage nic agents induce actomyosin-driven EC contraction tightly linked to myosin light chain (MLC) phosphorylation and microfilament reorganization, we exa mined the role of microtubule components in bovine EC barrier regulation. N ocodazole or vinblastine, inhibitors of microtubule polymerization, signifi cantly decreased transendothelial electrical resistance in a dose-dependent manner, whereas pretreatment with the microtubule stabilizer paclitaxel si gnificantly attenuated this effect. Decreases in transendothelial electrica l resistance induced by microtubule disruption correlated with increases in lung permeability in isolated ferret lung preparations as well as with inc reases in EC stress fiber content and MLC phosphorylation. The increases in MLC phosphorylation were attributed to decreases in myosin-specific phosph atase activity without significant increases in MLC kinase activity and wer e attenuated by paclitaxel or by several strategies (C3 exotoxin, toxin B, Rho kinase inhibition) to inhibit Rho GTPase. Together, these results sugge st that microtubule disruption initiates specific signaling pathways that c ross talk with microfilament networks, resulting in Rho-mediated EC contrac tility and barrier dysfunction.