Endothelial cells forming the inner lining of all blood vessels are actively involved in the regulation of the extravasation of fluid, macromolecules, hormones, and leukocytes. Only a few decades ago, it was thought that the endo-thelium functioned as a passive semipermeable barrier, but nowadays it is generally recognized that the endothelial cells actively and semiselectively play a pivotal role in the regulation of the passage of nutrients, hormones, and mac-romolecules. Over the past several years, the concept has emerged that the increase in endothelial permeability induced by vasoactive compounds, such as histamine and thrombin, is owing to intercellular gap formation. On the one hand, this is caused by contractile forces generated in the cell margins by actin- nonmuscle myosin interaction (1,2). On the other hand, alteration in cell-cell and cell-matrix interactions affect the endothelial barrier function (3).