Résumé :
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Communication n° 80. Skeletal muscle (SM) differentiation depends on Ca2+, but whether Ca2+ entry through voltage- dependent Ca2+ channels (VDCCs) contribute to SM differentiation or regeneration is yet unclear. Two types of VDCCs have been described in SM cells : i) L-type VDCCs generated by the CaV1.1/a1S subunit involved in excitation-contraction coupling, and ii) T-type VDCCs generated by the CaV3.2/a1H subunit that is present in developing SM. Recently, it has been proposed that T-type VDCCs participate to myoblast fusion and possibly to SM regeneration in humans (Bijlenga et al, PNAS 2000). To further document whether VDCCs play a role in muscle regeneration, we have investigated their properties in mouse myoblast fusion both using primary satellite cells cultured from adult SM cells and from the C2 cell line, that models satellite cells. The properties of VDCCs was analysed using the patch-clamp technique and the Ca2+ currents were recorded in the whole cell configuration. Neither T-type nor L-VDCC currents were detected in non-fused myoblasts. A typical slow activating and inactivating L-type Ca2+ current was measured in every myotubes, while a T-type Ca2+ current of small amplitude was recorded in ~ 30 % of the large myotubes (membrane capacitance > 100 pS). Further investigation was performed using the C2 cell line. Similarly, no VDCC current was recorded in C2 myoblasts and the appearance of Ca2+ currents was correlated with C2 myoblast fusion. Only slow L-type Ca2+ currents were measured in differentiated myotubes. T-type Ca2+ current was never detected in differentiating C2 cells although RT-PCR experiments identified CaV3.2/a1H subunit mRNA in differentiated C2 cultures (at day 3). Application of T-type VDCC blockers to C2 cultures, similarly to that obtained in primary satellite cell cultures, failed to significantly impair myoblast fusion (number and size of the myotubes). Altogether these results indicate that T-type VDCCs do not contribute to SM regeneration in mouse.
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