Figure 4

S1P interferes with the trophic effects of tumor necrosis factor (TNF)-α in L6 myotubes. (A) Myotube area was measured after 3 days of treatment with or without 15 ng/ml TNF-α, in the presence of 1 μmol/l exogenous S1P or 1 μmol/l inhibitor of the S1P receptor FTY720. Shown are the mean ± SE of 10 fields. +++ Different from control without drug: P < 0.0001; **different from TNF-α alone, P = 0.004. (B) Creatine kinase activity of myotubes treated for 3 days with TNF-α, without or with 1 μmol/l exogenous S1P, 1 μmol/l FTY720, or 10 μmol/l of the sphingosine kinase inhibitor dihydrosphingosine (DHS). Results are shown as the mean ± SE of 3 to 7 experiments performed in triplicate. +++ Different from control: P < 0.003; **different from TNF-α alone: P < 0.01, *P < 0.05. (C) Myotube area was measured after 3 days of treatment with 5 μmol/l C6 ceramide, without or with 1 μmol/l S1P or 10 μmol/l of the sphingosine kinase inhibitor dimethylsphingosine (DMS). Shown are the mean ± SE of 10 fields. ***Different from C6 ceramide alone: P < 0.005.