Journal of Applied Physiology AJP: Regulatory, Integrative and Comparative Physiology
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J Appl Physiol 73: 44S-50S, 1992;
8750-7587/92 $5.00
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Journal of Applied Physiology, Vol 73, Issue 2 44S-50S, Copyright © 1992 by American Physiological Society

ARTICLES

Skeletal muscle atrophy in response to 14 days of weightlessness: vastus medialis

X. J. Musacchia, J. M. Steffen, R. D. Fell, M. J. Dombrowski, V. W. Oganov and E. I. Ilyina-Kakueva
Department of Physiology and Biophysics, University of Louisville, Kentucky 40292.

The vastus medialis (VM) from rats after 14 days of microgravity on COSMOS 2044 (F) was compared with VM from tail-suspended hindlimb-unloaded rats (T) and ground controls, including vivarium (V), synchronous (S), and basal (B) animals. The VM is composed chiefly of fast-twitch fibers; however, it contains a deep portion closer to the bone with mixed slow- and fast-twitch fibers. In the mixed-fiber portion, type I and II fiber areas were significantly reduced in F animals. In the homogeneous portion with chiefly fast-twitch fibers, F rats also showed reductions in cross-sectional areas compared with T, V, and B but not S rats. Fiber densities (fibers/mm2) were greatest in VM from F rats. Capillary density changes paralleled fiber density changes. F animals have significantly greater density of capillaries in the mixed-fiber portion. Concentrations of protein, RNA, and DNA were highest in V controls, whereas F rats had the lowest level of total RNA. Lactate dehydrogenase activity, one measure of anaerobic capacity, was greater in F than in S rats. Citrate synthase activity, a measure of oxidative capacity, showed no significant differences between groups. Although triglyceride stores of VM were greater in F than in T rats, there were no significant differences from any of the control groups. It was concluded that VM wet weights may be a less sensitive measure of atrophy than the fiber area measurements. Fiber area decreases and fiber density increases in F animals were quantitatively comparable to those in soleus and extensor digitorum longus after 7 days of weightless flight in Spacelab 3. Our results suggest that VM shows measurable responses to weightlessness.




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