Perry Ben D, Wyckelsma Victoria L, Murphy Robyn M, Steward Collene H, Anderson Mitchell, Levinger Itamar, Petersen Aaron C, McKenna Michael J
Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.
Renal Division, Department of Medicine, Emory University, Atlanta, Georgia.
J Appl Physiol (1985). 2016 Nov 1;121(5):1074-1086. doi: 10.1152/japplphysiol.00558.2016. Epub 2016 Sep 15.
Physical training increases skeletal muscle Na,K-ATPase content (NKA) and improves exercise performance, but the effects of inactivity per se on NKA content and isoform abundance in human muscle are unknown. We investigated the effects of 23-day unilateral lower limb suspension (ULLS) and subsequent 4-wk resistance training (RT) on muscle function and NKA in 6 healthy adults, measuring quadriceps muscle peak torque; fatigue and venous [K] during intense one-legged cycling exercise; and skeletal muscle NKA content ([H]ouabain binding) and NKA isoform abundances (immunoblotting) in muscle homogenates (α, β) and in single fibers (α, β). In the unloaded leg after ULLS, quadriceps peak torque and cycling time to fatigue declined by 22 and 23%, respectively, which were restored with RT. Whole muscle NKA content and homogenate NKA α and β isoform abundances were unchanged with ULLS or RT. However, in single muscle fibers, NKA α in type I (-66%, P = 0.006) and β in type II fibers (-40%, P = 0.016) decreased after ULLS, with other NKA isoforms unchanged. After RT, NKA α (79%, P = 0.004) and β (35%, P = 0.01) increased in type II fibers, while α (76%, P = 0.028) and α (142%, P = 0.004) increased in type I fibers compared with post-ULLS. Despite considerably impaired muscle function and earlier fatigue onset, muscle NKA content and homogenate α and α abundances were unchanged, thus being resilient to inactivity induced by ULLS. Nonetheless, fiber type-specific downregulation with inactivity and upregulation with RT of several NKA isoforms indicate complex regulation of muscle NKA expression in humans.
体育锻炼可增加骨骼肌钠钾ATP酶（NKA）含量并改善运动表现，但不活动本身对人体肌肉中NKA含量和同工型丰度的影响尚不清楚。我们研究了23天单侧下肢悬吊（ULLS）及随后4周抗阻训练（RT）对6名健康成年人肌肉功能和NKA的影响，测量了股四头肌的峰值扭矩；在高强度单腿骑行运动期间的疲劳程度和静脉血[K]；以及肌肉匀浆（α、β）和单根肌纤维（α、β）中的骨骼肌NKA含量（[H]哇巴因结合）和NKA同工型丰度（免疫印迹）。在ULLS后，未负重腿的股四头肌峰值扭矩和骑行至疲劳的时间分别下降了22%和23%，而这些在RT后得以恢复。全肌肉NKA含量以及匀浆中NKA α和β同工型丰度在ULLS或RT后均未改变。然而，在单根肌纤维中，ULLS后I型纤维中的NKA α下降了66%（P = 0.006），II型纤维中的β下降了40%（P = 0.016），其他NKA同工型未改变。RT后，与ULLS后相比，II型纤维中的NKA α增加了79%（P = 0.004），β增加了35%（P = 0.01），而I型纤维中的α增加了76%（P = 0.028），α增加了142%（P = 0.004）。尽管肌肉功能明显受损且疲劳更早出现，但肌肉NKA含量以及匀浆中α和α丰度未改变，因此对ULLS诱导的不活动具有弹性。尽管如此，不活动导致的纤维类型特异性下调以及RT导致的几种NKA同工型上调表明人体肌肉中NKA表达的调节较为复杂。
