Tissue-specific Role of the Na,K-ATPase α2 Isozyme in Skeletal Muscle
Tissue-specific Role of the Na,K-ATPase α2 Isozyme in Skeletal Muscle
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DOI：
10.1074/jbc.m112.424663
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发表时间：
2013-01-11
影响因子：
4.8
通讯作者：
Heiny, Judith A.
中科院分区：
文献类型：
--
作者：
Radzyukevich, Tatiana L.;Neumann, Jonathon C.;Heiny, Judith A.
Na，K-ATP酶α 2同工酶是哺乳动物骨骼肌的主要Na，K-ATP酶。这种分布与大多数其他细胞相比是独特的，其他细胞主要表达Na，K-ATP酶α 1亚型，但其功能意义尚不清楚。我们开发了一种基因靶向小鼠（sk α 2（-/-）），其中α 2基因（Atp 1a 2）在骨骼肌中被敲除，并检查了运动表现，膜电位，收缩性和肌肉疲劳的后果。通过基因分型、蛋白质印迹和免疫组织化学证实靶向敲除。sk α 2（-/-）小鼠的骨骼肌细胞完全缺乏α 2蛋白，并且在横小管中没有α 2，在横小管中其表达通常增强。α 1亚型，这是正常的增强外肌膜，上调2.5倍，而不改变亚细胞靶向。SK α 2（-/-）小鼠在基础条件下显然是正常的，但当挑战跑步时显示出显著降低的运动能力。他们的骨骼肌产生较少的力量，无法增加力量以满足需求，并且表现出明显增加的疲劳敏感性。这些损伤影响快肌和慢肌类型。α 2的亚细胞靶向横小管是重要的这一作用。增加Na，K-ATP酶α 1含量不能完全补偿α 2的损失。通过用哇巴因选择性抑制α 2酶活性，在对照趾长伸肌中再现了sk α 2（-/-）肌肉增加的疲劳性。这些结果表明，Na，K-ATP酶α 2亚型在骨骼肌中发挥急性、亚型特异性作用。它的活动受肌肉使用的调节，使工作肌肉保持收缩和抵抗疲劳。
The Na,K-ATPase alpha 2 isozyme is the major Na, K-ATPase of mammalian skeletal muscle. This distribution is unique compared with most other cells, which express mainly the Na, K-ATPase alpha 1 isoform, but its functional significance is not known. We developed a gene-targeted mouse (sk alpha 2(-/-)) in which the alpha 2 gene (Atp1a2) is knocked out in the skeletal muscles, and examined the consequences for exercise performance, membrane potentials, contractility, and muscle fatigue. Targeted knockout was confirmed by genotyping, Western blot, and immunohistochemistry. Skeletal muscle cells of sk alpha 2(-/-) mice completely lack alpha 2 protein and have no alpha 2 in the transverse tubules, where its expression is normally enhanced. The alpha 1 isoform, which is normally enhanced on the outer sarcolemma, is up-regulated 2.5-fold without change in subcellular targeting. sk alpha 2(-/-) mice are apparently normal under basal conditions but show significantly reduced exercise capacity when challenged to run. Their skeletal muscles produce less force, are unable to increase force to match demand, and show significantly increased susceptibility to fatigue. The impairments affect both fast and slow muscle types. The subcellular targeting of alpha 2 to the transverse tubules is important for this role. Increasing Na, K-ATPase alpha 1 content cannot fully compensate for the loss of alpha 2. The increased fatigability of sk alpha 2(-/-) muscles is reproduced in control extensor digitorum longus muscles by selectively inhibiting alpha 2 enzyme activity with ouabain. These results demonstrate that the Na, K-ATPase alpha 2 isoform performs an acute, isoform-specific role in skeletal muscle. Its activity is regulated by muscle use and enables working muscles to maintain contraction and resist fatigue.