1. Laboratory of Physiology, School of Health Sciences, Toyohashi SOZO University, Toyohashi, Aichi, Japan;
2. Department of Sports Medicine, St. Marianna University School of Medicine, Kawasaki, Kanagawa, Japan;
3. Department of Physiology, Graduate School of Health Sciences, Toyohashi SOZO University, Toyohashi, Aichi, Japan;
4. Faculty of Education, Yamaguchi University, Yamaguchi-City, Yamaguchi, Japan;
5. Graduate School of Medicine, Osaka University, Toyonaka, Osaka, Japan;
6. Hirosaki Gakuin University, Hirosaki, Aomori, Japan.
Microcurrent electrical nerve stimulation (MENS) has been used to facilitate recovery from skeletal muscle injury. However, the effects of MENS on unloading-associated atrophied skeletal muscle remain unclear. Effects of MENS on the regrowing process of unloading-associated atrophied skeletal muscle were investigated. Male C57BL/6J mice (10-week old) were randomly assigned to untreated normal recovery (C) and MENS-treated (M) groups. Mice of both groups are subjected to continuous hindlimb suspension (HS) for 2 weeks followed by 7 days of ambulation recovery. Mice in M group were treated with MENS for 60 min 1, 3, and 5 days following HS, respectively, under anesthesia. The intensity, the frequency, and the pulse width of MENS were set at 10 μA, 0.3 Hz, and 250 msec, respectively. Soleus muscles were dissected before and immediately after, 1, 3 and 7 days after HS. Soleus muscle wet weight and protein content were decreased by HS. The regrowth of atrophied soleus muscle in M group was faster than that in C group. Decrease in the reloading-induced necrosis of atrophied soleus was facilitated by MENS. Significant increases in phosphorylated levels of p70 S6 kinase and protein kinase B (Akt) in M group were observed, compared with C group. These observations are consistent with that MENS facilitated regrowth of atrophied soleus muscle. MENS may be a potential extracellular stimulus to activate the intracellular signals involved in protein synthesis.
Keywords: skeletal muscle, atrophy, regrowth, microcurrent electrical nerve stimulation, intracellular signal, rehabilitation.