S1P enhances TRAP-induced TF activity expression. (A) Confluent monolayers of ECs were treated with varying concentrations of TRAP in the presence (•) and absence (○) of 4 μM S1P. (B) The monolayers were treated with varying concentrations of S1P in the presence (•) or absence (○) of 800 μM TRAP. TF activity on the EC surface was determined after 5 hours of stimulation as described in “Materials and methods.” These data represent the means ± SDs of 4 points per condition. Similar results were observed in 2 independent experiments using ECs of different lots.