Fig. 5. Stretch stimulates MHC expression in a TNF-- and p38-dependent manner. (A) Stretch stimulates MHC expression. C2C12 myoblasts were stretched for 6 hours and then incubated for an additional 24 or 48 hours without stretch. MHC (200 kDa) expression in myoblasts was compared with that of non-stretched controls by western blot analysis. (B) Stretch stimulation of MHC expression requires TNF- and p38. C2C12 myoblasts were stretched for 6 hours in culture medium that contained the TNF- neutralizing antibody (5 µg/ml), pre-immune IgG (5 µg/ml), SB-203580 (5 µM), or the DMSO vehicle (1 µl/ml), following a 30-minute pre-incubation period. Myoblasts were then incubated for an additional 48 hours without stretch. Western blot analysis was performed to evaluate MHC expression.