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抽动型转变。然而，有些纤维仍然是慢抽动类型。目前尚不清楚为什么肌球蛋白重链(MHC)表型的转化最初只在表达I型MHC的特定纤维中诱导。本研究旨在探讨机械和/或神经因素对纤维表型的影响。本实验研究了大鼠比目鱼肌MHC表达对机械活动抑制和神经活动抑制的反应。结果表明，两种实验模型均可诱导II型MHC基因和蛋白表达增加。I型和II型MHC共表达纤维的百分比分布增加。但仍可观察到表达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节。

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.