Wehrle U, Düsterhöft S, Pette D
Fakultät für Biologie, Universität Konstanz, Germany.
Differentiation. 1994 Nov;58(1):37-46. doi: 10.1046/j.1432-0436.1994.5810037.x.
Myotube cultures were established from satellite cells of three rat muscles of different fiber-type composition, slow-twitch soleus, diaphragm, and fast-twitch tibialis anterior (TA). Effects of chronic electrical stimulation were studied by exposing these cultures for up to 13 days to a stimulus pattern consisting of 250 ms impulse trains of 40 Hz, repeated every 4 s. Changes in myosin expression were assessed at the mRNA level by Northern blotting and in situ hybridization. Expression of slow myosin at the protein level was analysed by immunoblotting and immunohistochemistry with two antibodies, one specific to adult slow myosin, the other reacting with developmental and adult slow myosin heavy chain (MHCI) isoforms. In all three myotube cultures stimulation enhanced the mRNA and protein expression of a developmental isoform of slow myosin (MHCI). However, the three myotube cultures differed in the extent of the increase in MHCI. It was greatest in soleus-derived myotubes, least in TA-derived myotubes, and intermediate in diaphragm-derived myotubes. In addition to the increase in slow myosin, long-term stimulation led to an isoform switch, as indicated by an increase in myotubes reacting with the antibody specific for the adult MHCI. Our results suggest that enhanced contractile activity promotes the expression of the slow phenotype predetermined in satellite cells of slow-twitch, type I fibers. The different extents of increased slow myosin expression may thus be explained as reflecting different percentages of type I fibers and consequently of slow-type satellite cells in the corresponding donor muscles.
肌管培养物是从三种不同纤维类型组成的大鼠肌肉的卫星细胞建立的，即慢肌比目鱼肌、膈肌和快肌胫骨前肌（TA）。通过将这些培养物暴露于由40Hz的250ms脉冲串组成的刺激模式下长达13天，研究慢性电刺激的效果，该刺激模式每4秒重复一次。通过Northern印迹和原位杂交在mRNA水平评估肌球蛋白表达的变化。通过免疫印迹和免疫组织化学分析两种抗体在蛋白质水平上慢肌球蛋白的表达，一种抗体对成年慢肌球蛋白具有特异性，另一种与发育型和成年慢肌球蛋白重链（MHCI）同工型反应。在所有三种肌管培养物中，刺激均增强了慢肌球蛋白（MHCI）发育同工型的mRNA和蛋白质表达。然而，三种肌管培养物在MHCI增加的程度上有所不同。在比目鱼肌来源的肌管中增加最大，在TA来源的肌管中最小，在膈肌来源的肌管中处于中间水平。除了慢肌球蛋白增加外，长期刺激还导致同工型转换，这通过与成年MHCI特异性抗体反应的肌管增加来表明。我们的结果表明，增强的收缩活性促进了慢肌I型纤维卫星细胞中预先确定的慢表型的表达。因此，慢肌球蛋白表达增加的不同程度可以解释为反映了相应供体肌肉中I型纤维以及慢型卫星细胞的不同百分比。
