Effect of thrombin and PAR1 agonist peptide on barrier integrity. (A) Subconfluent cells were incubated for 3 hours with the indicated concentrations of thrombin (•) or PAR1 agonist peptide (○) (means ± SD, n = 3 for thrombin, n = 7 for PAR1, *P < .05 and **P < .005 compared to the lowest agonist concentration). (B) Subconfluent (top) or confluent (bottom) cells were incubated in serum-free growth medium containing 0.4% BSA for 3 hours with APC or the indicated concentrations of thrombin followed by permeability test in the subconfluent cells. In confluent cells permeability was tested before (□) and after an additional 10-minute incubation with 5 nM thrombin (▪) (means ± SD, n = 4, *P < .05 and **P < .005 compared to control). (C) Confluent cells were incubated in serum-free growth medium for 3 hours with carrier control (▪), APC (□), or 40 pM thrombin (▦) followed by a 30-minute incubation with control or 10 nM VEGF (means ± SD, n = 4, *P < .005 compared to carrier control).