Fig. 2. Transendothelial resistance (TER) and permeability for horse-radish peroxidase (HRP) of BCEC monolayers. TER was measured using a custom-made epithelial tissue voltohmmeter designed for Transwell filter inserts. The transendothelial transport of HRP to the lower compartment was assessed spectrophotometrically. OD values were representative of the traversed HRP and thus for the level of relative permeability. The standard deviations (error bars, n=4) are indicated.