Investigation of the mechanism responsible for the modulation of myosin heavy chain expression in muscle fibers.

重力卸载导致比目鱼肌纤维表型向快速抽搐型转变。然而，有些纤维仍然是慢肌纤维。目前尚不清楚为什么肌球蛋白重链（MHC）表型的转化仅在最初表达I型MHC的特定纤维中诱导。目前的研究是为了研究机械和/或神经因素对纤维表型的影响。研究了大鼠后肢悬吊和坐骨神经消融对2周机械活动和神经活动抑制对比目鱼肌MHC表达的影响。结果，两种实验模型均诱导ⅱ型MHC mRNA和蛋白表达升高。共表达I型和II型MHC的纤维的百分比分布增加。但仍然注意到表达纯I型MHC的纤维。提示ⅱ型MHC从头表达的原因可能受机械和神经活动等因素的调控。

Gravitational unloading causes a shift of fiber phenotype toward fast-twitch type in soleus muscle. However some fibers are remain slow-twitch type. It has not known why the transformation of myosin heavy chain (MHC) phenotype is induced only in specific fibers expressing type I MHC originally. The current study was performed to investigate the effects of mechanical and/or neural factors on the fiber phenotype. Responses of MHC expression in soleus muscles to 2-week inhibition of mechanical activity or neural activity by hindlimb suspension or ablation of sciatic nerve respectively, were studied in rats. As a result, both experimental model was induced the increase of the type II MHC mRNA and protein expression. And the % distribution of fibers co-expressing type I and II MHC was increased. But fibers expressing pure type I MHC were still noted. It was suggested that the cause for de novo expression of type II MHC might be regulated by mechanical and neural activity and other factors.