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1 Department of Human Nutrition, Foods and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0430; 2 Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75235-9040
Loss of the dystrophin-glycoprotein
complex from muscle sarcolemma in Duchenne's muscular dystrophy (DMD)
renders the membrane susceptible to mechanical injury, leaky to
Ca2+, and disrupts signaling, but the precise mechanism(s)
leading to the onset of DMD remain unclear. To assess the role of
mechanical injury in the onset of DMD, extensor digitorum longus (EDL)
muscles from C57 (control), mdx, and
mdx-utrophin-deficient [mdx:utrn(
/
); dystrophic] pups aged 9-12 days were subjected to an acute
stretch-injury or no-stretch protocol in vitro. Before the stretches,
isometric stress was attenuated for mdx:utrn(
/
) compared
with control muscles at all stimulation frequencies (P < 0.05). During the stretches, EDL muscles for each genotype
demonstrated similar mean stiffness values. After the stretches,
isometric stress during a tetanus was decreased significantly for both
mdx and mdx:utrn(
/
) muscles compared with
control muscles (P < 0.05). Membrane injury assessed
by uptake of procion orange dye was greater for dystrophic compared
with control EDL (P < 0.05), but, within each
genotype, the percentage of total cells taking up dye was not different for the no-stretch vs. stretch condition. These data suggest that the
sarcolemma of maturing dystrophic EDL muscles are resistant to acute
mechanical injury.
Duchenne's Muscular Dystrophy; mice; membrane damage
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