Type II muscle is more susceptible to contractile activity‐induced injury

Abstract

Contractile activity (CA) induces changes of cellular environment in cells, such as increased oxidative stress or inflammation. The changes are double‐ edged sword. When they are subtle and transient, they serve as signals of muscle growth induced by CA. However, cells could be damaged if CA‐induced oxidative stress and inflammation are excessive and prolonged. To date, it is unknown whether the responses to aerobic CA are fiber‐type specific. The aim of the study is to determine the effects of skeletal muscle types on inflammation and oxidative stress following aerobic CA. Type I (soleus) and Type II (white gastrocnemius) muscles from stimulated and contralateral non‐stimulated limbs were collected immediately and 6 hours after 21‐mintues of aerobic CA. Markers of oxidative stress (GSH, GSH/GSSG, oxidative‐modified proteins and lipids), inflammation (TNFα, IL6), growth factors (IGF1, MGF and myostatin), myogenesis (Myf5), and protein degradation (MuRF1) were evaluated. Independent t test was used to compare parameters between groups. Compared to type I muscles, type II muscles had lower basal level of oxidative stress (less accumulation of oxidative‐modified proteins and lipids, lower GSH level and GSH/GSSG), lower inflammation state (lower TNFα and IL6 levels), and lower levels of signals that stimulate the increase of muscle mass (lower levels of IGF1, MGF and Myf5, and higher level of myostatin and MuRF1). In response to aerobic CA, type II muscles showed earlier accumulation of oxidative damages than that in type I muscles. In addition, the Myf5 level in type I muscles elevated at 6 h after CA, but this change was not observed in type II muscles. Type II muscle is more susceptible to contractile activity‐induced injury. In addition, the regeneration capacity of type II muscle following aerobic CA is weaker than type I muscle.