title: Dissociation between short-term unloading and resistance training effects on skeletal muscle Na+,K+-ATPase, muscle function, and fatigue in humans.
abstract: 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 ([3H]ouabain binding) and NKA isoform abundances (immunoblotting) in muscle homogenates (α1-3, β1-2) and in single fibers (α1-3, β1). 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 α1-3and β1-2isoform abundances were unchanged with ULLS or RT. However, in single muscle fibers, NKA α3in type I (-66%, P = 0.006) and β1in type II fibers (-40%, P = 0.016) decreased after ULLS, with other NKA isoforms unchanged. After RT, NKA α1(79%, P = 0.004) and β1(35%, P = 0.01) increased in type II fibers, while α2(76%, P = 0.028) and α3(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 α1and α2abundances 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.
authors.affiliation: 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.
authors.forename: Ben D
authors.initials: BD
authors.lastname: Perry
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.
authors.forename: Victoria L
authors.initials: VL
authors.lastname: Wyckelsma
authors.affiliation: Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria, Australia; and.
authors.forename: Robyn M
authors.initials: RM
authors.lastname: Murphy
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.
authors.forename: Collene H
authors.initials: CH
authors.lastname: Steward
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.|Baker IDI Heart and Diabetes Institute, Melbourne, Victoria, Australia.
authors.forename: Mitchell
authors.initials: M
authors.lastname: Anderson
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.
authors.forename: Itamar
authors.initials: I
authors.lastname: Levinger
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia.
authors.forename: Aaron C
authors.initials: AC
authors.lastname: Petersen
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL), Clinical Exercise Science Program, Victoria University, Melbourne, Victoria, Australia; michael.mckenna@vu.edu.au.
authors.forename: Michael J
authors.identifier: 0000-0001-9998-0093
authors.initials: MJ
authors.lastname: McKenna
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D015444:Exercise / Q000502:physiology; D005221:Fatigue / Q000378:metabolism* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007866:Leg / Q000502:physiology; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology*; D010042:Ouabain / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D055070:Resistance Training / Q000379:methods; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D019415:Torque; D055815:Young Adult
chemical_list: D020033:Protein Isoforms; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Na+,K+ pump; disuse; fatigue; inactivity; strength training