Redox modulation of maximum force production of fast- and slow twitch skeletal muscles of rats and mice

We used intact fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles from rats and mice to test the hypothesis that exogenous app lication of an oxidant would increase maximum isometric force production (P -o) of slow-twitch muscles to a greater extent than fast-twitch skeletal mu scles. Exposure to an oxidant, hydrogen peroxide (H2O2; 100 muM to 5 mM, 30 min), affected P-o of rat muscles in a time- and dose-dependent manner. P- o of rat soleus muscles was increased by 8 +/- 1 (SE) and 14 +/- 1% (P < 0. 01) after incubation with 1 and 5 mM H2O2, respectively, whereas in mouse s oleus muscles P, was only increased after incubation with 580 <mu>M H2O2. P -o of rat EDL muscles was affected by H2O2 biphasically; initially there wa s a small increase (3 +/- 1%), but then P-o diminished significantly after 30 min of treatment. In contrast, all concentrations of H2O2 tested decreas ed P-o of mouse EDL muscles. A reductant, dithiothreitol (DTT; rat = 10 mM, mouse = 1 mM), was added to quench H2O2, and it reversed the potentiation in P-o in rat soleus but not in rat EDL muscles or in any H2O2-treated mous e muscles. After prolonged equilibration (30 min) with 5 mM H2O2 without pr ior activation, P-o was potentiated in rat soleus but not EDL muscles, demo nstrating that the effect of oxidation in the soleus muscles was also depen dent on the activation history of the muscle. The results of these experime nts demonstrate that P-o of both slow- and fast-twitch muscles from ratsand mice is modified by redox modulation, indicating that maximum P-o of mamma lian skeletal muscles is dependent on oxidation.