Effects of antithrombin forms on endothelial cell cycle transitions. Synchronized HUVEC cells (2 × 10⁶) were cultured with different antithrombin forms (20 μg/mL) in the presence or absence of bFGF (10 ng/mL) for 48 hours. Cells were fixed and stained with propidium iodide for detection of DNA and then analyzed by flow cytometry as detailed in “Materials and methods.” (A) Plots of the distribution of cells among the G₁, S, and G₂ phases of the cell cycle as reflected by their DNA content under the indicated culture conditions. (B) The percentage of cells in each cell cycle phase measured from the data in panel A and other experiments as mean values ± SD (bars) from 3 independent determinations. The different bar patterns represent from left to right the same sequence of conditions given in panel A. *A statistically significant difference from the control (P < .001).