S1P Tightens the Endothelial Barrier via a Cell Spreading Process Involving Rho Kinase

Sphingosine 1‐phosphate (S1P) induces a myriad of cellular events including an increase in endothelial barrier function. Previously, we demonstrated that S1P rapidly increases endothelial electrical resistance independently of homophilic VE‐cadherin binding. In the present study, we acquired a series of live‐cell images with phase‐contrast and differential interference‐contrast (DIC) optics of human umbilical vein endothelial cell (HUVEC) monolayers before and after the indicated treatments below. EGTA was added to the culture medium to disrupt homophilic VE‐cadherin binding, resulting in intercellular gaps between adjacent endothelial cells. Treatment with S1P alone or S1P plus MCDB‐131 to restore extracellular Ca2+ induced cells to spread and closed most of the intercellular gaps. Addition of MCDB‐131 alone affected cell spreading to a lesser extent. Pretreatment of cells with Latrunculin B, an inhibitor of actin polymerization, or Y‐27632, an inhibitor of Rho kinse, attenuated the cell spreading and increased electrical resistance induced by S1P. We conclude that S1P rapidly increases endothelial electrical resistance via cell spreading and that this process requires actin and Rho kinase. (Supported by HL‐68079)