Author(s): HUNG, Y.L., MACHIDA, S., Institution: JUNTENDO UNIVERSITY, Country: JAPAN, Abstract-ID: 2540

INTRODUCTION:
Skeletal muscles undergoe rapid and profound atrophy in response to inactivity such as limb immobilization and bed rest. In mature or old rats, muscle atrophy also occurs mainly through loss of the existing mass, including a reduction in the loss of myonuclei. It is likely that muscle satellite cells play an essential role in preventing age-related or inactive muscle atrophy, because skeletal muscle fibers are terminally differentiated (postmitotic) and require the proliferation of muscle satellite cells to provide new myonuclei for maintaining skeletal muscle. Endurance training increases the muscle satellite cell pool of skeletal muscles (1), but the effect of endurance training on muscle satellite cell proliferation is unclear. There is no information on how the proliferative function of muscle satellite cells is affected by endurance training and inactivity. This study aimed to examine the effects of endurance training and cast immobilization on the proliferative function of muscle satellite cells in vitro.
METHODS:
Female F344 rats (20 months old) were divided into three experimental groups: control (CON), endurance training (T), and immobilization (IM) groups. Rats in the T group were trained 5 days per week on a treadmill for 10 weeks, and rats in the IM group were subjected to cast immobilization of both lower extremities using casting tape for 10 days. After exercise training or cast immobilization, primary satellite cells were isolated from the quadriceps and gastrocnemius muscles of the rats. The effects of exercise training or cast immobilization on isolated satellite cell proliferation were examined by BrdU immunostaining.
RESULTS:
The number of isolated satellite cells was significantly higher in the T group than that in the CON group. On the other hand, the satellite cell number was reduced in the IM group compared to that in the CON group. The BrdU-positive cell ratio was significantly lower in the IM group than in the CON and T groups, but was not significantly different between the CON and T groups.
CONCLUSION:
These results suggest that inactivity in old female rats may reduce the proliferative function of muscle satellite cells and that exercise training increases the number of muscle satellite cells.

(1) M Kurosaka 1, H Naito, Y Ogura, S Machida, S Katamoto. Acta Physiol (Oxf). (2012); 205(1):159-66.