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Skeletal muscle adaptations to microgravity exposure in the mouse

¹Departments of Kinesiology and Applied Physiology, and ²Molecular, Cellular, and Developmental Biology, ⁴BioServe Space Technologies, University of Colorado, Boulder, Colorado 80309; ³National Aeronautics and Space Administration Ames Research Center, Moffett Field 94035; ⁵Metabolic Disorders Research, Amgen Incorporated, Thousand Oaks, California 91320; and ⁶Department of Bioengineering, Clemson University, Clemson, South Carolina 29634

Submitted 11 June 2003 ; accepted in final form 25 July 2003

To investigate the effects of microgravity on murine skeletal muscle fiber size, muscle contractile protein, and enzymatic activity, female C57BL/6J mice, aged 64 days, were divided into animal enclosure module (AEM) ground control and spaceflight (SF) treatment groups. SF animals were flown on the space shuttle Endeavour (STS-108/UF-1) and subjected to 11 days and 19 h of microgravity. Immunohistochemical analysis of muscle fiber cross-sectional area revealed that, in each of the muscles analyzed, mean muscle fiber cross-sectional area was significantly reduced (P < 0.0001) for all fiber types for SF vs. AEM control. In the soleus, immunohistochemical analysis of myosin heavy chain (MHC) isoform expression revealed a significant increase in the percentage of muscle fibers expressing MHC IIx and MHC IIb (P < 0.05). For the gastrocnemius and plantaris, no significant changes in MHC isoform expression were observed. For the muscles analyzed, no alterations in MHC I or MHC IIa protein expression were observed. Enzymatic analysis of the gastrocnemius revealed a significant decrease in citrate synthase activity in SF vs. AEM control.

animal enclosure module

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