Résumé :
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Duchenne muscular dystrophy (DMD) is a progressive disease characterized by the absence of dystrophin due to a defect in the p21 band of the X chromosome. Lack of dystrophin expression causes muscle degeneration by a mechanism that remains elusive but has long been attributed to membrane defects and/or increased permeability to Ca2+. A number of studies have reported chronic elevation in intracellular Ca2+ concentration in skeletal muscle fibers or in cultured myotubes from DMD patients and mdx mice. Two of the pathways that might be involved in the Ca2+ overload are store operated channels (SOC) and stretch activated channels (SAC). Earlier results suggest that both channels are controlled, at least partly, by the Ca2+-independent form of phospholipase A2 (iPLA2). Several groups also reported that this increment in intracellular Ca2+ concentration modulates reactive oxygen species production. In the present study, we investigated the effect of doxorubicin (Dox), a chemotherapeutic agent reported to inhibit iPLA2, on the activity of iPLA2 and its consequences on Ca2+ handling and ROS production in EDL-MDX-2 myotubes. PED-6, a fluorogenic probe, was used to determine PLA2 activity while 45Ca2+ influx experiments and luminometry using targeted aequorin expression were used to determine the effect of Dox on Ca2+ handling. To track changes in ROS production the fluorogenic probe DCFH-DA was used. Dox inhibited PLA2 in clinically relevant concentrations (1-30 ?M), blocked the entry through SAC almost completely but had minimal effects on SOC. It also increased ROS production dose dependently in the first 5 min of introduction and subsequently inhibited its production. Dox effects on fatigue characteristics in isolated fast and slow twitch muscles were also assayed. Further investigations are ongoing to better understand the complex mechanism of action of Dox on skeletal muscle function.
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