Résumé :
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Communication n° 284 Caveolin is a membrane scaffolding protein which associates with and regulates a variety of signaling proteins, including ion channels. Caveolin-3 (Cav-3) is the major striated muscle isoform of caveolin and its deficiency is responsible for skeletal muscle disorders, such as limb girdle muscular dystrophy 1C. Recent results suggest that Cav-3 is involved in intracellular Ca2+ homeostasis regulation and we recently showed that disruption of caveolae and T-tubules, which constitute Cav-3-enriched membrane domains, by cholesterol depletion, led to a significant alteration of L-type Ca2+ current and of voltage-evoked Ca2+ transients in fetal skeletal muscle. In the current study, we investigated the possible existence of a functional interaction between Cav-3 and L-type Ca2+ channels. Using the whole-cell configuration of the patch-clamp technique, we analyzed L-type Ca2+ current in mouse primary cultured skeletal myotubes in control conditions and after over-expression of Cav-3P104L, a dystrophy-associated mutant that leads to a severe loss of the endogenous protein. Double immunolabelling experiments were also performed. Results showed that the maximum conductance of L-type Ca2+ channels was significantly reduced by ~54% in myotubes expressing Cav-3P104L whereas voltage-dependence parameters (V1/2 and k) remained unchanged. Immunolabelling confirmed that Cav-3 no longer reached the sarcolemma in myotubes expressing Cav-3P104L, being either undetectable or confined to vesicles. Additionally, in control conditions, Cav-3 and L-type Ca2+ channels appeared co-localized at the surface membrane and in the T-tubule network of myotubes and adult skeletal muscle cells. Taken together, our present results suggest that Cav-3 functionally interacts with L-type Ca2+ channels in skeletal muscle cells and that an alteration of L-type current might be involved in the physiopathological mechanisms of caveolinopathies.
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