Fig. 4. Stretch activation of myogenic differentiation markers is mediated by p38. C2C12 myoblasts were pre-incubated (30 minutes) and stretched for the indicated periods in growth medium that contained the p38 inhibitor SB203580 (5 µM) or the same volume of DMSO (1 µl/ml), which was used as vehicle for SB203580. Western blot analysis was conducted to determine MEF2C phosphorylation and the expression level of myogenin and p21. -actin was monitored as the loading control.