Ca2+ signalling 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 (Ins P₃^-) sensitive stores contributes the remaining 20% to the maximal [Ca²⁺]_i increment. Furthermore, we found that ACh-induced mobilization from Ins P₃-sensitive stores also develops in embryonic chick myotubes. The differential importance of the Ca²⁺ signalling pathways activated by ACh during myogenesis is discussed.