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缩型转变。但有些纤维仍为慢缩型。肌球蛋白重链（myosin heavy chain，MHC）表型的转化为何只在表达I型MHC的特定纤维中被诱导，目前尚不清楚。本研究旨在探讨机械和/或神经因素对纤维表型的影响。用后肢悬吊法和坐骨神经切断法分别对大鼠比目鱼肌的机械活动和神经活动抑制2周后，比目鱼肌MHC表达的变化进行了研究。结果表明，两种实验模型均诱导了II型MHC mRNA和蛋白表达的增加。并且共表达I型和II型MHC的纤维的%分布增加。但仍可见表达纯I型MHC的纤维。提示Ⅱ型MHC的重新表达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.