Effect of IS on the viability of MC3T3-E1 cells. Cell number was measured 24 h after the addition of IS at concentrations ranging from 0.1 to 1.5 mM and was expressed as the percentage of control cells not pretreated with IS (open bar). The cell toxicity of IS was found to be dose dependent. The data represent the mean ± SEM from 8 replicates in each group. *P < 0.05 vs. control cells.