Differing Responses of Satellite Cell Activity to Exercise Training in Rat Skeletal Muscle

Abstract

Abstract.[Purpose] The present study examined satellite cell and hepatocyte growth factor (HGF) responses to exercise intensity in the rat soleus muscle.[Methods] HGF levels assessed during postnatal growth of the gastrocnemius muscle. Depression of HGF levels occurred up to postnatal week 4, so 4-weekold rats were used the exercise training experiment. Rats walked or ran at speeds of 16 or 24 m/min, at -16% grade, 30 min/trial. Soleus muscles were removed after 72 h. Animals were injected with the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU) 1 h before sampling. The right soleus muscle was used for immunofluorescence, and the left soleus muscle was used to measure HGF protein levels.[Result] HGF levels were unchanged, although numbers of BrdU-positive nuclei increased 2.4-fold in rats with exercise training.[Conclusion] The relationship between activation of satellite cells and HGF production after exercise training remains unclear. However, this study indicates the exercise intensity necessary to activate satellite cells. In the future, this result may facilitate the creation of exercise training intensity as an index of satellite cell activity for muscle strength training.

Myogenic cell response to muscle contraction with short electrical stimulation

“…In the present study, the plantaris muscle wet weight to body weight, and the mRNA expressions of HGF and MyoD , plateaued at 8 weeks of age during postnatal growth. These results are consistent with those of previous studies using HGF enzyme-linked immunosorbent assay and immunohistochemistry 11 , 15 , 16 ) . Therefore, 8-week-old rats in which the effect of growth was small were used in the subsequent study.…”

“…MyoD and myogenin belong to a class of myogenic differentiation factors, which are expressed in myogenic cells during proliferation and differentiation, and in the present study, expression of these genes indicated satellite cell activation 11 , 17 , 18 , 19 ) . The mRNA expressions of MyoD , myogenin , and c-Me t immediately increased after the 5-min electrical stimulation.…”

“…Although the precise mechanism of satellite cell activation induced by hepatocyte growth factor (HGF) is unclear, it is one of the key events in this recovery process 1 , 2 , 3 , 4 , 5 ) . In fact, previous studies using experimental animal models have demonstrated that satellite cell activation and HGF production are induced by activities that cause continuous muscle contraction, such as high-intensity running for 30 min, synergist muscle ablation, contralateral continuous overloading by ablation of a sciatic nerve, and reloading 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ) . However, in clinical physical therapy, it is difficult to perform high-intensity exercise for 30 min or longer.…”

MyoD, Myogenin and Myosin Heavy Chain mRNA Expression in Rat Skeletal Muscle after a Single Session of Low-Intensity Treadmill Exercise

“…In this study (24 m/min, -16°, 30 min), however, MyoD mRNA expression showed no changes, and myogenin mRNA expression at P24 was about 1.7-fold that in CON, although the difference was not significant. Our previous study showed that BrdU-positive cells were significantly elevated using the same exercise protocol in 4-wk-old rats 18) . The difference between the present and previous studies was apparently due to age, as the number of satellite cells decreased in SOL, and the number of satellite cell activated by exercise is known to decrease with aging 3) .…”

“…Rats in the experimental groups performed running at 24 m/min on a treadmill with 16° decline for 30 min. The exercise protocol was based on that used in previous studies 3, [16][17][18] . After the exercise, rats were returned to their cages and given ad libital access to food and water.…”