Elevation of the expression of the inositol-1,4,5-trisphosphate receptors and increase of calcium signaling in response to ATP during differentiation of skeletal myoblasts C2C12 into myotubes

The expression levels of inositol-1,4,5-trisphosphate receptors (InsP3R) and cytoplasmic free calcium concentration ([Ca2+]c) changes in response to ATP in cultured skeletal myoblasts C2C12, in myoblasts at different stages of differentiation into myotubes, and in differentiated multinucleated myotubes have been determined. Using reverse transcription and real-time polymerase chain reaction we have shown that during differentiation of myoblasts into myotubes the expression of all three InsP3R increased 2–2.5-fold and at all stages of differentiation the expression levels of InsP3R2 and InsP3R3 were nearly equal to each other and 1.5–2 times higher than the expression level of InsP3R1. The kinetics of calcium signal in myotubes is characterized by higher maximal [Ca2+]c rise and more prolonged second phase in comparison with myoblasts. The data obtained provide evidence in favor of the increasing role of InsP3-dependent calcium mobilization at the first stages of skeletal muscles maturation.