Ultrathin sections of HUVEC cells exposed to (A, B) 1 pmol/L VBL and (C) 24 hours after removing the VBL-containing medium. (A, B) Round-shaped endothelial cell displaying numerous bundles of thickened microfilaments distributed in the cytoplasm (arrow). (C) Endothelial cell showing normal distribution of cytoskeleton organelles. Bar (A), (C) = 16.6 μm; (B) = 0.5 μm.