ABSTRACT
Objective To study the effects of tumor necrosis factord (TNF ?)on degradation of long lived protein in cultured myotubes, myoblasts were proliferated in tissue block culture and fused into myotubes. Methods Then the protein in myotubes was radiolabelled with L [3,5 3 H] tyrosine. Myotubes were either cultured with TNF ? 2000U/mL or without TNF ?, and 12h, 24h, 36h, 48h later, the amounts of L [3,5 3 H] tyrosine in culture medium and cells were determined, and the degradation rates of long lived protein were calculated. Other myotubes were cultured either with 50?mol/mL proteasome inhibitor MG132 or 50?mol/mL MG132 and TNF ? 2000U/mL, and long lived proteolytic rates were calculated by the same method after 24h culture. Results The long lived proteolytic rates in myotubes cultured with TNF ? were increased significantly at all time points compared with control group ( P