Dynamic modulation of barrier function. Endothelial cells achieve a semi-permeable barrier by interacting with each other in a dynamic fashion through specific receptors called cadherins. In this example (figure), confluent HUVEC monolayer was treated with increasing doses of thrombin resulting in a concentration-dependent decrease in cell index, which has been shown to correlate with disruption of the homotypic cadherin interactions and transient contraction of the cells due to formation of actin stress fibers.