ADAPTATION OF RAT GASTROCNEMIUS-MUSCLES TO 2 WEEKS OF CENTRIFUGATION - MYOFIBERS AND EXTRACELLULAR-MATRIX

Background: The effect of 2 wk of exposure to centrifugation (2G) on g astrocnemius muscles of rats was investigated by morphometric and comp uter-assisted image analysis of muscle fiber areas and non-contractile tissue components (extracellular matrix). Results: Muscle atrophy was seen in the myofibers from 2G rats which had decreased in cross-secti onal area by 26%. In contrast, the non-contractile tissue component ac tually increased by 13%. These results were compared with soleus muscl e atrophy seen following 2 wk of unloading by tail-suspension. In all cases, the extracellular matrix increased in proportion to the decreas e in fiber area. A theoretical model was developed to assess the effec t of changes in myofiber cross-sectional area on the relative content of the extracellular matrix. The experimental results from both rat ga strocnemius and soleus muscles were consistent with the model with sli ght variations due to the known differences in connective tissue conte nt of different muscles in the rat. Conclusion: Thus, the gastrocnemiu s muscle atrophy seen after 2 wk of centrifugation results from loss o f contractile and other myofiber specific proteins while the extracell ular matrix remains relatively constant. The loss in myofiber content was greater than expected from changes in muscle wet weight and more t han required to adapt to a decrease in body weight.