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Am J Physiol Cell Physiol 295: C458-C467, 2008. First published June 4, 2008; doi:10.1152/ajpcell.00497.2007
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MUSCLE CELL BIOLOGY AND CELL MOTILITY

Essential role of satellite cells in the growth of rat soleus muscle fibers

Fuminori Kawano,1 Yoshiaki Takeno,1 Naoya Nakai,1 Yoko Higo,2 Masahiro Terada,2 Takashi Ohira,2 Ikuya Nonaka,3 and Yoshinobu Ohira1,2

Graduate School of 1Medicine and 2Frontier Bioscience, Osaka University, Osaka; and 3National Center for Neurology and Psychiatry, Tokyo, Japan

Submitted 19 October 2007 ; accepted in final form 29 May 2008

Effects of gravitational loading or unloading on the growth-associated increase in the cross-sectional area and length of fibers, as well as the total fiber number, in soleus muscle were studied in rats. Furthermore, the roles of satellite cells and myonuclei in growth of these properties were also investigated. The hindlimb unloading by tail suspension was performed in newborn rats from postnatal day 4 to month 3 with or without 3-mo reloading. The morphological properties were measured in whole muscle and/or single fibers sampled from tendon to tendon. Growth-associated increases of soleus weight and fiber cross-sectional area in the unloaded group were ~68% and 69% less than the age-matched controls. However, the increases of number and length of fibers were not influenced by unloading. Growth-related increases of the number of quiescent satellite cells and myonuclei were inhibited by unloading. And the growth-related decrease of mitotically active satellite cells, seen even in controls (20%, P > 0.05), was also stimulated (80%). The increase of myonuclei during 3-mo unloading was only 40 times vs. 92 times in controls. Inhibited increase of myonuclear number was not related to apoptosis. The size of myonuclear domain in the unloaded group was less and that of single nuclei, which was decreased by growth, was larger than controls. However, all of these parameters, inhibited by unloading, were increased toward the control levels generally by reloading. It is suggested that the satellite cell-related stimulation in response to gravitational loading plays an essential role in the cross-sectional growth of soleus muscle fibers.

gravitational loading/unloading; antigravity muscle


Address for reprint requests and other correspondence: Y. Ohira, Section of Applied Physiology, Graduate School of Medicine, Osaka Univ., Toyonaka City, Osaka, 560-0043, Japan (e-mail: ohira{at}space.hss.osaka-u.ac.jp)






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