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Ontogenetic, gravity-dependent development of rat soleus muscleWe tested the hypothesis that rat soleus muscle fiber growth and changes in myosin phenotype during the postnatal, preweaning period would be largely independent of weight bearing. The hindlimbs of one group of pups were unloaded intermittently from postnatal day 4 to day 21: the pups were isolated from the dam for 5 h during unloading and returned for nursing for 1 h. Control pups were either maintained with the dam as normal or put on an alternating feeding schedule as described above. The enlargement of mass (approximately 3 times), increase in myonuclear number (approximately 1.6 times) and myonuclear domain (approximately 2.6 times), and transformation toward a slow fiber phenotype (from 56 to 70% fibers expressing type I myosin heavy chain) observed in controls were inhibited by hindlimb unloading. These properties were normalized to control levels or higher within 1 mo of reambulation beginning immediately after the unloading period. Therefore, chronic unloading essentially stopped the ontogenetic developmental processes of 1) net increase in DNA available for transcription, 2) increase in amount of cytoplasm sustained by that DNA pool, and 3) normal transition of myosin isoforms that occur in some fibers from birth to weaning. It is concluded that normal ontogenetic development of a postural muscle is highly dependent on the gravitational environment even during the early postnatal period, when full weight-bearing activity is not routine.
Document ID
20040112527
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ohira, Y.
(National Institute of Fitness and Sports Shiromizu 2, Kanoya City, Kagoshima Prefecture 891-2393, Japan)
Tanaka, T.
Yoshinaga, T.
Kawano, F.
Nomura, T.
Nonaka, I.
Allen, D. L.
Roy, R. R.
Edgerton, V. R.
Date Acquired
August 21, 2013
Publication Date
April 1, 2001
Publication Information
Publication: American journal of physiology. Cell physiology
Volume: 280
Issue: 4
ISSN: 0363-6143
Subject Category
Life Sciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Musculoskeletal

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