Thrombin-induced permeability. HUV-EC-C monolayers cultured on collagen IV-coated microporous cell culture inserts were either left untreated (n = 3; ▪) or exposed to 5 U/mL thrombin (n = 3; ▨) for 15 minutes. Monolayer permeability was measured by TEFF and was expressed as the mean fold change in fluid flux ± standard deviation. The mean pretreatment fluid flux values for untreated and thrombin-treated monolayers were 84 and 141 (μL/min)/cm², respectively. Statistically significant differences between the mean responses of treated and time-matched control monolayers are depicted as follows: **P < .01.