Effect of filipin on caveolar structure and TF expression. Monolayers of WI-38 fibroblasts were treated with a control vehicle (A) or filipin (5 μg/mL) (B) for 15 minutes at 37°C. Cells were fixed, sectioned, stained for TF by immunogold, and visualized under transmission electron microscope. Thin arrows point out gold particles whereas arrowheads point out caveolae. Bar indicates 200 nm. (C) Control or filipin-treated monolayers were incubated with either ¹²⁵I-VIIa (10 nM) or unlabeled VIIa (10 nM) and factor X (175 nM) to determine VIIa binding and TF-VIIa activity (n = 4, mean ± SE). * denotes significantly differs (P < .05) from the control.