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time course of myosin heavy chain transitions in neonatal rats: importance of innervation and thyroid stateDuring the postnatal period, rat limb muscles adapt to weight bearing via the replacement of embryonic (Emb) and neonatal (Neo) myosin heavy chains (MHCs) by the adult isoforms. Our aim was to characterize this transition in terms of the six MHC isoforms expressed in skeletal muscle and to determine the importance of innervation and thyroid hormone status on the attainment of the adult MHC phenotype. Neonatal rats were made hypothyroid via propylthiouracil (PTU) injection. In normal and PTU subgroups, leg muscles were unilaterally denervated at 15 days of age. The MHC profiles of plantaris (PLN) and soleus (Sol) muscles were determined at 7, 14, 23, and 30 days postpartum. At day 7, the Sol MHC profile was 55% type I, 30% Emb, and 10% Neo; in the PLN, the pattern was 60% Neo and 25% Emb. By day 30 the Sol and PLN had essentially attained an adult MHC profile in the controls. PTU augmented slow MHC expression in the Sol, whereas in the PLN it markedly repressed IIb MHC by retaining neonatal MHC expression. Denervation blunted the upregulation of IIb in the PLN and of Type I in the Sol and shifted the pattern to greater expression of IIa and IIx MHCs in both muscles. In contrast to previous observations, these findings collectively suggest that both an intact thyroid and innervation state are obligatory for the attainment of the adult MHC phenotype, particularly in fast-twitch muscles.
Document ID
20040142005
Document Type
Reprint (Version printed in journal)
Authors
Adams, G. R.
(University of California Irvine California 92697-4560, United States)
McCue, S. A.
Zeng, M.
Baldwin, K. M.
Date Acquired
August 22, 2013
Publication Date
April 1, 1999
Publication Information
Publication: The American journal of physiology
Volume: 276
Issue: 4 Pt 2
ISSN: 0002-9513
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: NS-33483
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Musculoskeletal