Young R B, Denome R M, Achtymichuk G W
Eur J Cell Biol. 1981 Dec;26(1):184-7.
After approximately one week in culture, embryonic chick skeletal muscle cells are at a steady state with respect to myosin heavy chain (MHC) concentration and synthesis rate. Muscle cells normally synthesize MHC at a maximum rate of 2.3 X 10 4 MHC/min/nucleus and contain approximately 3 X 10 7 MHC/nucleus. These cells also contain approximately 3500 copies/nucleus of MHC mRNA associated with polysomes and 1600 copies/nucleus of MHC mRNA localized in the nonpolysomal fraction. To determine if nonpolysomal MHC mRNA in mature muscle cultures could be recruited into active translation complexes when MHC synthesis was stimulated, muscle cultures were treated with the Ca 2+ ionophore, A23187 (0-1 micro M). The MHC synthesis rate was stimulated by 25 to 50% relative to stimulation of the rate of total protein synthesis in the presence of A23187, but this stimulation was blocked when 10 microgram/ml actinomycin D was also present. These results suggest that even though 30% of MHC mRNA is not actively engaged in MHC synthesis in mature muscle cultures, stimulation of MHC synthesis by A23187 results from transcription of new MHC mRNA rather than from utilization of pre-existing mRNA.
在培养大约一周后，鸡胚骨骼肌细胞的肌球蛋白重链（MHC）浓度和合成速率处于稳定状态。肌肉细胞通常以最高2.3×10⁴ MHC/分钟/细胞核的速率合成MHC，每个细胞核中含有约3×10⁷ MHC。这些细胞还含有约3500个与多核糖体相关的MHC mRNA拷贝/细胞核以及1600个位于非多核糖体部分的MHC mRNA拷贝/细胞核。为了确定当MHC合成受到刺激时，成熟肌肉培养物中的非多核糖体MHC mRNA是否可以被募集到活跃的翻译复合物中，用Ca²⁺离子载体A23187（0 - 1微摩尔）处理肌肉培养物。相对于在A23187存在下总蛋白质合成速率的刺激，MHC合成速率提高了25%至50%，但当同时存在10微克/毫升放线菌素D时，这种刺激被阻断。这些结果表明，尽管在成熟肌肉培养物中30%的MHC mRNA没有积极参与MHC合成，但A23187对MHC合成的刺激是由新的MHC mRNA转录引起的，而不是来自于对预先存在的mRNA的利用。
