Résumé
Tumor necrosis factor-alpha (TNF) diminishes specific force of skeletal muscle. To address the mechanism of this response, we tested the hypothesis that TNF acts via the type 1 (TNFR1) receptor subtype to increase oxidant activity and thereby depress myofibrillar function. Experiments showed that a single intraperitoneal dose of TNF (100 mu g/kg) increased cytosolic oxidant activity (P < 0.05) and depressed maximal force of male ICR mouse diaphragm by similar to 25% within 1 h, a deficit that persisted for 48 h. Pretreating animals with the antioxidant Trolox (10 mg/kg) lessened oxidant activity (P < 0.05) and abolished contractile losses in TNF-treated muscle (P < 0.05). Genetic TNFR1 deficiency prevented the rise in oxidant activity and fall in force stimulated by TNF; type 2 TNF receptor deficiency did not. TNF effects on muscle function were evident at the myofibrillar level. Chemically permeabilized muscle fibers from TNF-treated animals had lower maximal Ca2+-activated force (P < 0.02) with no change in Ca2+ sensitivity or shortening velocity. We conclude that TNF acts via TNFR1 to stimulate oxidant activity and depress specific force. TNF effects on force are caused, at least in part, by decrements in function of calcium-activated myofibrillar proteins.