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Force-Velocity and Power Characteristics of Rat Soleus Muscle Fibers after Hindlimb SuspensionThe effects of 1, 2, and 3 wk of Hindlimb Suspension (HS) on force-velocity and power characteristics of single rat soleus fibers were determined. After 1, 2, or 3 wk of HS, small fiber bundles were isolated, placed in skinning solution, and stored at -20 C until studied. Single fibers were isolated and placed between a motor arm and force transducer, functional properties were studied, and fiber protein content was subsequently analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Additional fibers were isolated from soleus of control and after 1 and 3 wk of HS, and fiber type distribution and myosin light chain stoichiometry were determined from SDS-PAGE analysis. After 1 wk of HS, percent type I fibers declined from 82 to 74%, whereas hybrid fibers increased from 10 to 18%. Percent fast type 11 fibers increased from 8% in control and 1 wk of HS to 26% by 3 wk of HS. Most fibers showed an increased unloaded maximal shortening velocity (V(sub 0)), but myosin heavy chain remained entirely slow type I. The mechanism for increased V(sub 0) is unknown. There was a progressive decrease in fiber diameter (14, 30, and 38%) and peak force (38, 56, and 63%) after 1, 2, and 3 wk of HS, respectively. One week of HS resulted in a shift of the force-velocity curve, and between 2 and 3 wk of HS the curve shifted further such that V(sub 0) was higher than control at all relative loads less than 45% peak isometric force. Peak absolute power output of soleus fibers progressively decreased through 2 wk of HS but showed no further change at 3 wk. The results suggest that between 2 and 3 wk the HS-induced alterations in the force-velocity relationship act to maintain the power output of single soleus fibers despite a continued reduction in fiber force.
Document ID
19980008764
Acquisition Source
Ames Research Center
Document Type
Contractor Report (CR)
Authors
McDonald, K. S.
(Marquette Univ. Milwaukee, WI United States)
Blaser, C. A.
(Marquette Univ. Milwaukee, WI United States)
Fitts, R. H.
(Marquette Univ. Milwaukee, WI United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1994
Publication Information
Publisher: American Physiological Society
ISSN: 0161-7567
Subject Category
Life Sciences (General)
Report/Patent Number
NASA-CR-204849
NAS 1.26:204849
Funding Number(s)
CONTRACT_GRANT: NAG2-212
Distribution Limits
Public
Copyright
Public Use Permitted.
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