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A new animal model for modulating myosin isoform expression by altered mechanical activityThe purpose of this study was to develop a new rodent model that is capable of delineating the importance of mechanical loading on myosin heavy chain (MHC) isoform expression of the plantar and dorsi flexor muscles of the ankle. The essential components of this system include 1) stimulating electrodes that are chronically implanted into a muscle, allowing for the control of the activation pattern of the target muscle(s); 2) a training apparatus that translates the moment of the ankle into a linear force; and 3) a computer-controlled Cambridge 310 ergometer. The isovelocity profile of the ergometer ensured that the medial gastrocnemius (MG) produced forces that were > 90% of maximal isometric force (Po), and the eccentric contractions of the tibialis anterior (TA) were typically 120% of Po. Both the concentric and eccentric training programs produced statistically significant increases in the muscle mass of the MG (approximately 15%) and TA (approximately 7%) as well as a decrease in myofibrillar adenosinetriphosphatase activity. Both the white and red regions of the MG and TA exhibited significant increases in the relative content of the type IIa MHC and concomitant decreases in type IIb MHC expression. Although the red regions of the MG and red TA contained approximately 10% type I MHC, the training programs did not affect this isoform. It appears that when a fast-twitch muscle is stimulated at a high frequency (100 Hz) and required to contract either concentrically or eccentrically under high loading conditions, the expression of the type IIa MHC isoform will be upregulated, whereas that of the type IIb MHC will be concomitantly downregulated.
Document ID
20050000598
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Caiozzo, V. J.
(College of Medicine, University of California Irvine 92717)
Ma, E.
McCue, S. A.
Smith, E.
Herrick, R. E.
Baldwin, K. M.
Date Acquired
August 22, 2013
Publication Date
October 1, 1992
Publication Information
Publication: Journal of applied physiology (Bethesda, Md. : 1985)
Volume: 73
Issue: 4
ISSN: 8750-7587
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: AR-30346
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Musculoskeletal
Non-NASA Center

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