ASGSB 2003 Annual Meeting Abstracts


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Passive Stretch Inhibits Central Core-like Lesion Formation in Soleus Muscles of Anesthetized, Hindlimb Suspended Unloaded Rats  D.V. Baewer1, M. Hoffman2, J.G. Romatowski2, B.D. Curry1, J.L.W. Bain1, R.H. Fitts2, and D.A. Riley11Dept of Cell Biology, Neurobiology & Anatomy, Medical College of Wisconsin, Milwaukee WI, 2Dept of Biology, Marquette University, Milwaukee, WI.

   Hindlimb suspension unloading (HSU) is a ground-based model designed to simulate the effects of microgravity unloading on the musculoskeletal system.  Gravity causes the hind foot of the rat to droop, bringing the ankle to a ~90 angle.  The normal weight bearing angle is 30 dorsiflexion.  The foot drop posture decreases the contraction range of the foot plantar flexors, such as soleus.  Previously, we reported that 12 days of HSU caused central core-like lesions (CCLs) and atrophy of rat soleus muscle fibers [Riley et al. JAP 69:58, 1990].  CCLs are focal regions lacking myofibrillar ATPase activity and slow myosin immunostaining and showing sarcomere disruption at the ultrastructural level.  Stretching the soleus muscles of HSU rats by splinting the ankle at 30 for 10 or 20 total min per day decreased lesioned fiber percentage by 90% and lessened atrophy 50%.  Bilateral soleus EMG recording revealed increased contractile activity during splinting (mean total activity MV-sec increased 169% and train duration 580%).  To isolate the effects of stretch from contractile activity, muscle contractions were eliminated by whole animal anesthesia with isofluorane during splinting.  The right legs of HSU, male Sprague Dawley rats (2616 g, n=7) were splinted at 30 for 10 minutes per day.  The percentage of fibers with CCL lesions (10.82.7%) was significantly lower (p<0.05) than that in the non-splinted side (23.43.9%).   Decreases in muscle wet weight and fiber area were not inhibited.  The percentage of fiber area lesioned was quantitated by thresholding digital microscopic images with Metamorph software.  Lesion size (area%) was, on the average, significantly smaller in splinted muscles (0.15.5%) than that (0.25.04%) in the non-splinted muscles (p<0.05).  These results indicate that passive muscle length is important for the maintenance of sarcomere stability. 

(Supported by NASA NCC2-1373 and NASA EPSCoR NCC5-581)

 

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