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Response of slow and fast muscle to hypothyroidism: maximal shortening velocity and myosin isoformsThis study examined both the shortening velocity and myosin isoform distribution of slow- (soleus) and fast-twitch (plantaris) skeletal muscles under hypothyroid conditions. Adult female Sprague-Dawley rats were randomly assigned to one of two groups: control (n = 7) or hypothyroid (n = 7). In both muscles, the relative contents of native slow myosin (SM) and type I myosin heavy chain (MHC) increased in response to the hypothyroid treatment. The effects were such that the hypothyroid soleus muscle expressed only the native SM and type I MHC isoforms while repressing native intermediate myosin and type IIA MHC. In the plantaris, the relative content of native SM and type I MHC isoforms increased from 5 to 13% and from 4 to 10% of the total myosin pool, respectively. Maximal shortening velocity of the soleus and plantaris as measured by the slack test decreased by 32 and 19%, respectively, in response to hypothyroidism. In contrast, maximal shortening velocity as estimated by force-velocity data decreased only in the soleus (-19%). No significant change was observed for the plantaris.
Document ID
Document Type
Reprint (Version printed in journal)
Caiozzo, V. J. (University of California Irvine 92717)
Herrick, R. E.
Baldwin, K. M.
Date Acquired
August 22, 2013
Publication Date
July 1, 1992
Publication Information
Publication: The American journal of physiology
Volume: 263
Issue: 1 Pt 1
ISSN: 0002-9513
Subject Category
Life Sciences (General)
Funding Number(s)
Distribution Limits
Non-NASA Center
NASA Discipline Musculoskeletal