Rosser B W, Waldbillig D M, Lovo S D, Armstrong J D, Bandman E
Department of Anatomy and Cell Biology, University of Saskatchewan College of Medicine, Saskatoon, Canada.
Anat Rec. 1995 Aug;242(4):462-70. doi: 10.1002/ar.1092420404.
The pectoralis muscle of the chicken contains fast-twitch glycolytic fibers, which during development undergo a transformation in their myosin heavy chain (MyHC) content from embryonic to a neonatal to an adult isoform (Bandman et al., 1990). Little, however, is known of MyHC expression within the ends of these or other muscle fibers. Here we test the hypothesis that the tapered ends of mature skeletal muscle fibers contain a less mature MyHC isoform than that typically found throughout their lengths.
We apply an ammoniacal silver histological stain for endomysium and monoclonal antibodies against neonatal and adult MyHCs of chicken pectoralis to transverse serial sections of pectoralis from five mature chickens. The "lesser fiber diameters" of populations of fibers from each bird are also measured.
Most (approximately 81.8%) of the small (< 12 microns) and none of the larger (> 20 microns) diameter fibers contain the neonatal MyHC. Following these smaller fibers through serial sections, we show that they are the tapered ends of the larger fibers. Whereas neonatal MyHC is restricted to the tapered fiber ends, adult MyHC is present throughout the entire lengths of all fibers. We also demonstrate acetylcholinesterase (AChE) activity at some of these fiber ends.
We postulate that longitudinal growth of myofibrils in adult muscle is characterized by the sequential expression of MyHC isoforms similar to that observed in rapidly growing muscle and that the presence of the neurotransmitter hydrolase AChE at the tapered fiber ends may be related to the retention of neonatal MyHC.
鸡的胸肌含有快速糖酵解纤维，在发育过程中，其肌球蛋白重链（MyHC）含量会从胚胎型转变为新生儿型再到成年型异构体（Bandman等人，1990年）。然而，对于这些或其他肌纤维末端的MyHC表达情况却知之甚少。在此，我们检验这样一个假设：成熟骨骼肌纤维的锥形末端所含的MyHC异构体不如在其整个长度中通常发现的那样成熟。
我们对五只成年鸡胸肌的横向连续切片应用氨银组织学染色来显示肌内膜，并使用针对鸡胸肌新生儿型和成年型MyHC的单克隆抗体。还测量了每只鸡的纤维群体中“较小纤维直径”。
大多数（约81.8%）直径小（<12微米）的纤维含有新生儿型MyHC，而直径大（>20微米）的纤维则无一含有。通过连续切片追踪这些较细的纤维，我们发现它们是较粗纤维的锥形末端。新生儿型MyHC局限于纤维的锥形末端，而成年型MyHC则存在于所有纤维的整个长度中。我们还在其中一些纤维末端证实了乙酰胆碱酯酶（AChE）活性。
我们推测成年肌肉中肌原纤维的纵向生长特点是MyHC异构体的顺序表达，类似于在快速生长肌肉中观察到的情况，并且在纤维锥形末端存在神经递质水解酶AChE可能与新生儿型MyHC的保留有关。
