EFFECT OF HYDROGEN-PEROXIDE AND DITHIOTHREITOL ON CONTRACTILE FUNCTION OF SINGLE SKELETAL-MUSCLE FIBERS FROM THE MOUSE

1.We used intact single fibres from a mouse foot muscle to study the r ole of oxidation-reduction in the modulation of contractile function. 2. The oxidant hydrogen peroxide (H2O2, 100-300 mu M) for brief period s did not change myoplasmic Ca2+ concentrations ([Ca2+](i)) during sub maximal tetani. However, force increased by 27 % during the same contr actions. 3. The effects of H2O2 were time dependent. Prolonged exposur es resulted in increased resting and tetanic [Ca2+](i), while force wa s significantly diminished. The force decline was mainly due to reduce d myofibrillar Ca2+ sensitivity. There was also evidence of altered sa rcoplasmic reticulum (SR) function: passive Ca2+ leak was increased an d Ca2+ uptake was decreased. 4. The reductant dithiothreitol (DTT, 0.5 -1 mM) did not change tetanic [Ca2+](i), but decreased force by over 4 0%. This was completely reversed by subsequent incubations with H2O2. The force decline induced by prolonged exposure to H2O2 was reversed b y subsequent exposure to DTT. 5. These results show that the elements of the contractile machinery are differentially responsive to changes in the oxidation-reduction balance of the muscle fibres. Myofibrillar Ca2+ sensitivity appears to be especially susceptible, while the SR fu nctions (Ca2+ leak and uptake) are less so.