Résumé :
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Communiation n° 215 Duchenne Muscular Dystrophy results from the lack of dystrophin, a cytoskeletal protein associated with the inner surface membrane, in skeletal muscle. The absence of dystrophin induces an abnormal increase of sarcolemmal calcium influx through cationic channels. Using a dystrophin-deficient Sol8 myogenic subline we have previously shown that forced expression of mini-or full-length dystrophin rapidly restores calcium handling. The resting steady-state level of calcium ions is lowered as well as the amplitudes of calcium transients during a depolarisation. We are now intending to identify the calcium signalling systems directly involved in this recovery of calcium handling. Among sarcolemmal calcium channels that could be regulated by dystrophin, Store-Operated Calcium (SOC) channels could be responsible of a maintained calcium influx during muscle cells activity. By cytofluorimetry, we have observed that depletion of calcium stores (sarcoplasmic reticulum) leads to a transmembrane cationic influx, which is 2-fold higher in dystrophin-deficient myotubes. Store-Operated Calcium Entries (SOCE) results in a cytosolic calcium elevation that is modulated by 2-APB an activator and inhibitor of SOC channel. In myotubes expressing minidystrophin, the entries are faster than in dystrophin deficient myotubes that display more sustained entries. The use of a recombinante aequorine targeted to mitochondria have shown that these SOCE also lead to calcium entry into mitochondria, a major calcium buffer of muscle cells. These intramitochondrial entries are smaller in myotubes expressing minidystrophin. Cytosolic entries are also modulated by FCCP a protonophore that depolarised mitochondria. We propose that minidystrophin could improve calcium homeostasis and cell survival through a better control of SOCE and mitochondria loading. This control may be performed thanks to alpha-syntrophin, which could links dystrophin and SOC channel.
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