Reiser P J, Kline W O, Vaghy P L
Department of Oral Biology, The Ohio State University, Columbus 43210-1218, USA.
J Appl Physiol (1985). 1997 Apr;82(4):1250-5. doi: 10.1152/jappl.1997.82.4.1250.
Fast-twitch skeletal muscles contain more neuronal-type nitric oxide synthase (nNOS) than slow-twitch muscles because nNOS is present only in fast (type II) muscle fibers. Chronic in vivo electrical stimulation of tibialis anterior and extensor digitorum longus muscles of rabbits was used as a method of inducing fast-to-slow fiber type transformation. We have studied whether an increase in muscle contractile activity induced by electrical stimulation alters nNOS expression, and if so, whether the nNOS expression decreases to the levels present in slow muscles. Changes in the expression of myosin heavy chain isoforms and maximum velocity of shortening of skinned fibers indicated characteristic fast-to-slow fiber type transformation after 3 wk of stimulation. At the same time, activity of NOS doubled in the stimulated muscles, and this correlated with an increase in the expression of nNOS shown by immunoblot analysis. These data suggest that nNOS expression in skeletal muscle is regulated by muscle activity and that this regulation does not necessarily follow the fast-twitch and slow-twitch pattern during the dynamic phase of phenotype transformation.
快肌骨骼肌比慢肌含有更多的神经元型一氧化氮合酶（nNOS），因为nNOS仅存在于快肌（II型）肌纤维中。采用慢性体内电刺激兔胫骨前肌和趾长伸肌的方法来诱导快肌纤维向慢肌纤维类型转变。我们研究了电刺激诱导的肌肉收缩活动增加是否会改变nNOS的表达，如果会改变，nNOS的表达是否会降低到慢肌中的水平。肌球蛋白重链亚型表达的变化以及脱膜纤维缩短的最大速度表明，刺激3周后出现了典型的快肌纤维向慢肌纤维类型转变。与此同时，受刺激肌肉中一氧化氮合酶的活性增加了一倍，这与免疫印迹分析显示的nNOS表达增加相关。这些数据表明，骨骼肌中nNOS的表达受肌肉活动调节，并且在表型转变的动态阶段，这种调节不一定遵循快肌和慢肌模式。
