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CELLULAR AND MOLECULAR

Greater Susceptibility of the Sarcoplasmic Reticulum to H₂O₂ Injuries in Diaphragm Muscle from mdx Mice

Université de Nantes, Centre National de la Recherche Scientifique, Unité Mixte Recherche 6204, Biotechnologie, Biocatalyse et Biorégulation, Faculté des Sciences et des Techniques, Nantes, Cedex, France

The aim of the present study was to investigate the direct effects of a reactive oxygen species, H₂O₂, on the contractile function and sarcoplasmic reticulum properties of dystrophin-deficient diaphragm using chemically skinned fibers and sarcoplasmic reticulum vesicle preparations. The results obtained using Triton X-100-skinned fibers demonstrate that exposure to 1mMH₂O₂ had similar effects on the maximal Ca²⁺-activated tension and on the Ca²⁺ sensitivity of the contractile apparatus of diaphragm fibers in Bl10 and mdx mice. The effects of H₂O₂ were also assessed on sarcoplasmic reticulum function using saponin-skinned fibers and sarcoplasmic reticulum vesicle preparations. We found that H₂O₂ induced changes in sarcoplasmic reticulum properties, particularly in the Ca²⁺ pump function. The most important finding was that diaphragm muscle from mdx mice displayed increased sensitivity to the oxidant. Furthermore, in isolated superfused diaphragm muscle from mdx mice, the data demonstrate that the amount of superoxide anion produced under fatiguing conditions was increased. Our study shows that the sarcoplasmic reticulum, and the Ca²⁺ pump in particular, in dystrophin-deficient muscles display increased susceptibility to H₂O₂ injuries. This suggests that free radicals might, therefore, be involved in the pathophysiological pathway and dysregulation of Ca²⁺ homeostasis of muscular dystrophy.

Address correspondence to: Dr. Corinne Huchet-Cadiou, Université de Nantes, Centre National de la Recherche Scientifique, UMR 6204, Biotechnologie, Biocatalyse et Biorégulation, Faculté des Sciences et des Techniques, 2 rue de la Houssinière, BP 92208, F-44322 Nantes, Cedex 03, France. E-mail: corinne.cadiou{at}univ-nantes.fr

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