title: Hydrogen peroxide increases depolarization-induced contraction of mechanically skinned slow twitch fibres from rat skeletal muscles.
abstract: The effect of exogenous hydrogen peroxide (H(2)O(2)) on excitation-contraction (E-C) coupling and sarcoplasmic reticulum (SR) function was compared in mechanically skinned slow twitch fibres (prepared from the soleus muscles) and fast twitch fibres (prepared from the extensor digitorum longus; EDL muscles) of adult rats. Equilibration (5 min) with 1 mM H(2)O(2) diminished the ability of the Ca(2+)-depleted SR to reload Ca(2+) in both slow (P < 0.01) and fast twitch fibres (P < 0.05) compared to control. Under conditions when all Ca(2+) uptake was prevented, 1 mM H(2)O(2) increased SR Ca(2+) "leak" in fast twitch fibres by 24 +/- 5 % (P < 0.05), but leak was not altered in slow twitch fibres. Treatment with 1 mM H(2)O(2) also increased the peak force of low [caffeine] contracture by approximately 45% in both fibre types compared to control (P < 0.01), which could be partly reversed following treatment with 10 mM dithiothreitol (DTT). The changes in SR function caused by 1 mM H(2)O(2) were associated with an approximately 65% increase in the peak height of depolarization-induced contractile response (DICR) in slow twitch fibres, compared to control (no H(2)O(2); P < 0.05). In contrast, peak contractile force of fast twitch fibres was not altered by 1 mM H(2)O(2) treatment. Equilibration with 5 mM H(2)O(2) induced a spontaneous force response in both slow and fast twitch fibres, which could be partly reversed by 2 min treatment with 10 mM DTT. Peak DICR was also increased approximately 40% by 5 mM H(2)O(2) in slow twitch fibres compared to control (no H(2)O(2); P < 0.05). Our results indicate that exogenous H(2)O(2) increases depolarization-induced contraction of mechanically skinned slow but not fast twitch fibres. The increase in depolarization-induced contraction in slow twitch fibres might be mediated by an increased SR Ca(2+) release during contraction and/or an increase in Ca(2+) sensitivity.
authors.affiliation: Department of Physiology, University of Melbourne, Victoria 3010, Australia.
authors.forename: David R
authors.initials: DR
authors.lastname: Plant
authors.forename: Gordon S
authors.initials: GS
authors.lastname: Lynch
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
mesh_terms: D000818:Animals; D004594:Electrophysiology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects* / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000502:physiology*; D016877:Oxidants / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000502:physiology
chemical_list: D016877:Oxidants; D006861:Hydrogen Peroxide