Effect of IS addition on ALP activity in MC3T3-E1 cells. ALP activity was suppressed by IS at concentrations greater than 1 mM. ALP activity is expressed as nanomoles of p-nitrophenol released per milligram of protein. ALP, alkaline phosphatase *P < 0.05 vs. control cells at each time point. The data represent the mean ± SEM (n = 6 for each group).