Reduced soleus muscle injury at long muscle length during contraction in the rat |
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Authors: | Seigo Usami Tomoyuki Kurose Yuko Ando Minoru Hayakawa Seiichi Kawamata |
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Institution: | (1) Department of Anatomy and Histology, Graduate School of Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan; |
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Abstract: | Muscle injury was studied to test the hypotheses that maintaining the soleus muscle at a long muscle length during contraction
prevents muscle injuries and that the prevention of initial muscle injuries reduces subsequent muscle damage. The rat sciatic
nerve was stimulated for 30 min with plantar or dorsal flexion of the foot, and the time course of contraction-induced injuries
was examined. The soleus muscle injuries were first classified into one of five types, and the percentages of aberrant sarcomere
areas observed in the soleus muscle were then separately quantified by electron microscopy at 0, 1, 6, 12, and 24 h (n = 3) post-stimulation. At a short muscle length (plantar flexion) during contraction, the soleus muscle showed sarcomere
hypercontraction (9.8 ± 2.5%, mean ± standard error) and Z-band disarrangement (31.0 ± 4.5%) at 0 h, sarcomere hypercontraction
(6.7 ± 1.9%), Z-band disarrangement (28.0 ± 4.9%), and sarcomere hyperstretching (1.3 ± 1.3%) at 1 h, the absence of sarcomere
hypercontraction, but Z-band disarrangement (6.7 ± 1.9%) and sarcomere hyperstretching (5.0 ± 1.8%) at 6 h, and myofilament
disorganization at 12 and 24 h (5.2 ± 1.5 and 2.5 ± 1.0%, respectively). In contrast, the soleus muscles at a long muscle
length (dorsal flexion) during contraction using a self-made brace showed alterations in 1.2–2.4% of sarcomeres at 0 h and
afterwards. Desmin disappeared, and α-actinin immunostaining was weaker in areas of sarcomere hypercontraction, whereas dystrophin
was always detected along the sarcoplasmic membrane, suggesting that the integrity of the sarcolemma was intact. These results
indicate that initial and subsequent muscle injuries were significantly reduced at long muscle length during contraction,
probably through the prevention of sarcomere hypercontraction, and that initial muscle injuries rapidly progress to other
injuries or normal structure. |
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