Effect of IS on MC3-T3 cell apoptosis, determined by FACS analysis. (A) Cells were incubated with various concentrations of IS for 24 h, after which they were harvested, the DNA was stained with propidium iodide, and the cells were analyzed using FACS. (B) IS increased the proportion of apoptotic cells in MC3-T3 cells. *P < 0.05 vs. control cells. The data represent the mean ± SEM (n = 3 for each group).