Applied Physiology, Nutrition, and Metabolism, Ahead of Print.
Contraction-induced adaptations in skeletal muscles are well characterized in vivo, but the underlying cellular mechanisms are still not completely understood. Cultured human myotubes represent an essential model system for human skeletal muscle that can be modulated ex vivo, but they are quiescent and do not contract unless being stimulated. Stimulation can be achieved by innervation of human myotubes in vitro by co-culturing with embryonic rat spinal cord, or by replacing motor neuron activation by electrical pulse stimulation (EPS). Effects of these two in vitro approaches, innervation and EPS, were characterized with respects to the expression of myosin heavy chains (MyHCs) and metabolism of glucose and oleic acid in cultured human myotubes. Adherent human myotubes were either innervated with rat spinal cord segments or exposed to EPS. The expression pattern of MyHCs was assessed by quantitative polymerase chain reaction, immunoblotting, and immunofluorescence, while the metabolism of glucose and oleic acid were studied using radiolabelled substrates. Innervation and EPS promoted differentiation towards different fiber types in human myotubes. Expression of the slow MyHC-1 isoform was reduced in innervated myotubes, whereas it remained unaltered in EPS-treated cells. Expression of both fast isoforms (MyHC-2A and MyHC-2X) tended to decrease in EPS-treated cells. Both approaches induced a more oxidative phenotype, reflected in increased CO2 production from both glucose and oleic acid. Novelty: Innervation and EPS favour differentiation into different fiber types in human myotubes. Both innervation and EPS promote a metabolically more oxidative phenotype in human myotubes.

中文翻译：

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神经支配和电脉冲刺激——对人体骨骼肌细胞的体外影响

应用生理学、营养学和代谢，提前出版。
骨骼肌收缩诱导的适应在体内得到了很好的表征，但潜在的细胞机制仍未完全了解。培养的人类肌管代表了人类骨骼肌的基本模型系统，可以在体外进行调节，但它们是静止的，除非受到刺激，否则不会收缩。通过与胚胎大鼠脊髓共培养，或通过电脉冲刺激 (EPS) 替代运动神经元激活，体外人肌管的神经支配可以实现刺激。这两种体外方法神经支配和 EPS 的影响在肌球蛋白重链 (MyHC) 的表达以及葡萄糖和油酸在培养的人肌管中的代谢方面进行了表征。粘附的人类肌管要么受大鼠脊髓节段支配，要么暴露于 EPS。MyHCs 的表达模式通过定量聚合酶链反应、免疫印迹和免疫荧光进行评估，同时使用放射性标记底物研究葡萄糖和油酸的代谢。神经支配和 EPS 促进了人类肌管向不同纤维类型的分化。慢 MyHC-1 亚型在受神经支配的肌管中的表达降低，而在 EPS 处理的细胞中保持不变。两种快速同种型（MyHC-2A 和 MyHC-2X）的表达在 EPS 处理的细胞中趋于降低。这两种方法都诱导了更具氧化性的表型，这反映在葡萄糖和油酸产生的二氧化碳增加。新颖性：神经支配和 EPS 有利于分化为人类肌管中的不同纤维类型。神经支配和 EPS 都促进了人类肌管中代谢性更强的氧化表型。