Levels of HDL-associated S1P dictate the magnitude of the TEER response. Confluent EC monolayers were incubated with native HDL (72 nM S1P) or HDL containing varying amounts of exogenously added S1P. HDL was added to achieve a final concentration of 250 μg protein/ml. As a control, monolayers were incubated with the vehicle buffer, 0.03 mM EDTA in Dulbecco's PBS (Control). Each of the TEER tracings shown is an average from two replicates per treatment. Impedance values were normalized by dividing each value by the level of impedance measured just prior to the addition of effectors. The results depicted are representative of two independent experiments.