Carlsson E, Thornell L E
Cell Tissue Res. 1987 Apr;248(1):169-80. doi: 10.1007/BF01239978.
The fine structure of the M-band in soleus (SOL) and extensor digitorum longus (EDL) muscles in newborn and four-week-old rats was studied using electron-microscopic techniques. In newborn rats, all myotubes and fibres in both muscles had an identical myofibrillar appearance. A five-line M-band pattern was seen in longitudinal sections and distinct M-bridges in cross-sections. The Z-discs were of medium width. On the other hand, in four-week-old rats, different muscle fibre types were observed on the basis of their myofibrillar pattern. In SOL two fibre types were distinguished in longitudinal sections. One had a four-line M-band pattern and very broad Z-discs, whereas the other type had five lines in the M-band and broad Z-discs. In EDL, three different myofibrillar patterns were observed. The M-bands were composed of three, four or five lines. Fibres had either thin, broad or medium Z-disc widths, respectively. In cross-sections of the SOL muscle one group of fibres showed indistinct M-bridges, whereas distinct M-bridges were seen in the other fibres and in all observed EDL muscle fibres. We conclude that initially there seems to be a single intrinsic program for M-band genesis; this program becomes modified upon the induction of functionally differentiated fibres.
运用电子显微镜技术研究了新生和四周龄大鼠比目鱼肌（SOL）和趾长伸肌（EDL）中M带的精细结构。在新生大鼠中，两块肌肉中的所有肌管和肌纤维都具有相同的肌原纤维外观。在纵切面上可见五条线的M带模式，在横切面上可见明显的M桥。Z盘宽度中等。另一方面，在四周龄大鼠中，根据肌原纤维模式观察到不同的肌纤维类型。在比目鱼肌纵切面上可区分出两种纤维类型。一种具有四条线的M带模式和非常宽的Z盘，而另一种类型的M带中有五条线且Z盘较宽。在趾长伸肌中，观察到三种不同的肌原纤维模式。M带由三条、四条或五条线组成。纤维的Z盘宽度分别为薄、宽或中等。在比目鱼肌的横切面上，一组纤维的M桥不明显，而在其他纤维以及所有观察到的趾长伸肌纤维中可见明显的M桥。我们得出结论，最初似乎存在一个单一的M带形成内在程序；该程序在功能分化纤维诱导后发生改变。
