CA2+ SIGNALING PATHWAYS ACTIVATED BY ACETYLCHOLINE IN MOUSE C2C12 MYOTUBES

In mouse C2C12 myotubes acetylcholine (ACh) elevates the concentration of myoplasmic Ca2+ ([Ca2+](i)) by inducing Ca2+ influx through transmittergated and voltage-gated channels, and by mobilizing Ca2+ from internal stores. The relative contribution of each of these ACh-activated sources to the global [Ca2+](i) elevation was estimated. We found that Ca2+ entry through voltage- and ACh-gated channels accounts for roughly 80% of the total [Ca2+](i) increment, while mobilization from internal caffeine-sensitive and inositol-trisphosphate- (InsP(3)-) sensitive stores contributes the remaining 20% to the maximal [Ca2+](i) increment. Furthermore, we found that ACh-induced mobilization from InsP(3)-sensitive stores also develops in embryonic chick myotubes. The differential importance of the Ca2+ signalling pathways activated by ACh during myogenesis is discussed.