S1P enhances thrombin-induced TF mRNA expression. Confluent monolayers of ECs were treated with or without 2.5 nM thrombin, 4 μM S1P, or 2.5 nM thrombin plus 4 μM S1P for 0.5 to 5 hours. The cells were then harvested and processed for detection of TF mRNA by Northern blot analysis. The upper panel shows the total RNA samples as detected by ethidium bromide staining; intact 18S and 28S rRNA bands served as control of equal RNA loading for Northern blot analysis. The results shown are representative of 3 independent experiments.