The goals of this research were to a) characterize the protein-function
relationships of skeletal muscle single fibers from the mouse hindlimb b) examine
mouse-strain related differences in myosin heavy chain composition (MHC) and
single fiber contractile function, and c) quantify changes in fiber size and
contractile function in response to 7 days of non-weight bearing. This research is
significant because mechanistic approaches to understanding relationships between
muscle protein expression, contractile function, and mechanical loading will likely
benefit from a transition from the traditional laboratory rat to genetically modified
mouse models.
The methods used in this research feature an in vitro skinned-fiber
preparation and single-fiber gel electrophoresis. Hindlimb muscles of mice were
excised, and dissected into smaller bundles from which single muscle fibers were
isolated. Single fibers were placed in skinning solution that permeabilized the
fiber's membrane. The ends of skinned single muscle segments were attached to
stainless steel troughs, which were connected to an isometric force transducer and a
direct-current position motor. This system allowed the measurement of the fiber's
cross-sectional area (CSA), peak isometric force (P���), and unloaded maximal
shortening velocity (V���) during maximal Ca�����-activating. The identification of the
fiber's MHC content was subsequently achieved by electrophoresis of a sample of
each fiber segment.
The results showed that the C57BL/6 mouse soleus muscle contains a
MHC composition (20% type I) that is dramatically different than the ICR and
CBA/J mouse strains (50% type I, respectively). Type I fibers from the C57BL/6
mouse had V��� that was 25% lower than type I fibers from ICR and CBA/J mice.
Following 7 days of hindlimb suspension (HS) all strains experienced significant
soleus muscle and single-fiber atrophy and decreases in the absolute and specific
(force/fiber CSA) of type I and II fibers. However, type I fibers from C57BL/6
mice showed no change in V��� whereas type I fibers from ICR and CBA/J showed
increased V���.
In conclusion, this research demonstrates that unlike the rat and human
models of non-weight bearing, mouse soleus type I and II fibers are equally
affected by HS with respect to decreases in fiber CSA and force. However, type I
fiber V��� was elevated only in mouse strains with solei containing at least 50% type
I MHC. These findings challenge the current view that non-weight bearing affects
slow fibers more than fast fibers, and suggests that changes in single fiber
contractile function with HS may be influenced in part by the MHC distribution of
the muscle. / Graduation date: 2003
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/31160 |
| Date | 20 May 2002 |
| Creators | Stelzer, Julian E. (Julian Emanuel) |
| Contributors | Widrick, Jeffrey J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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