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Sostaric S, Petersen AC, Goodman CA, Gong X, Aw TJ, Brown MJ, Garnham A, Steward CH, Murphy KT, Carey KA, Leppik J, Fraser SF, Cameron-Smith D, Krum H, Snow RJ, McKenna MJ. Oral digoxin effects on exercise performance, K + regulation and skeletal muscle Na + ,K + -ATPase in healthy humans. J Physiol 2022; 600:3749-3774. [PMID: 35837833 PMCID: PMC9541254 DOI: 10.1113/jp283017] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 07/08/2022] [Indexed: 11/30/2022] Open
Abstract
Abstract We investigated whether digoxin lowered muscle Na+,K+‐ATPase (NKA), impaired muscle performance and exacerbated exercise K+ disturbances. Ten healthy adults ingested digoxin (0.25 mg; DIG) or placebo (CON) for 14 days and performed quadriceps strength and fatiguability, finger flexion (FF, 105%peak‐workrate, 3 × 1 min, fourth bout to fatigue) and leg cycling (LC, 10 min at 33% VO2peak and 67% VO2peak, 90% VO2peak to fatigue) trials using a double‐blind, crossover, randomised, counter‐balanced design. Arterial (a) and antecubital venous (v) blood was sampled (FF, LC) and muscle biopsied (LC, rest, 67% VO2peak, fatigue, 3 h after exercise). In DIG, in resting muscle, [3H]‐ouabain binding site content (OB‐Fab) was unchanged; however, bound‐digoxin removal with Digibind revealed total ouabain binding (OB+Fab) increased (8.2%, P = 0.047), indicating 7.6% NKA–digoxin occupancy. Quadriceps muscle strength declined in DIG (−4.3%, P = 0.010) but fatiguability was unchanged. During LC, in DIG (main effects), time to fatigue and [K+]a were unchanged, whilst [K+]v was lower (P = 0.042) and [K+]a‐v greater (P = 0.004) than in CON; with exercise (main effects), muscle OB‐Fab was increased at 67% VO2peak (per wet‐weight, P = 0.005; per protein P = 0.001) and at fatigue (per protein, P = 0.003), whilst [K+]a, [K+]v and [K+]a‐v were each increased at fatigue (P = 0.001). During FF, in DIG (main effects), time to fatigue, [K+]a, [K+]v and [K+]a‐v were unchanged; with exercise (main effects), plasma [K+]a, [K+]v, [K+]a‐v and muscle K+ efflux were all increased at fatigue (P = 0.001). Thus, muscle strength declined, but functional muscle NKA content was preserved during DIG, despite elevated plasma digoxin and muscle NKA–digoxin occupancy, with K+ disturbances and fatiguability unchanged.
![]() Key points The Na+,K+‐ATPase (NKA) is vital in regulating skeletal muscle extracellular potassium concentration ([K+]), excitability and plasma [K+] and thereby also in modulating fatigue during intense contractions.
NKA is inhibited by digoxin, which in cardiac patients lowers muscle functional NKA content ([3H]‐ouabain binding) and exacerbates K+ disturbances during exercise. In healthy adults, we found that digoxin at clinical levels surprisingly did not reduce functional muscle NKA content, whilst digoxin removal by Digibind antibody revealed an ∼8% increased muscle total NKA content. Accordingly, digoxin did not exacerbate arterial plasma [K+] disturbances or worsen fatigue during intense exercise, although quadriceps muscle strength was reduced. Thus, digoxin treatment in healthy participants elevated serum digoxin, but muscle functional NKA content was preserved, whilst K+ disturbances and fatigue with intense exercise were unchanged. This resilience to digoxin NKA inhibition is consistent with the importance of NKA in preserving K+ regulation and muscle function.
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Affiliation(s)
- Simon Sostaric
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Aaron C Petersen
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Craig A Goodman
- Institute for Health and Sport, Victoria University, Melbourne, Australia.,Centre for Muscle Research, Department of Anatomy and Physiology, University of Melbourne, Parkville, Australia
| | - Xiaofei Gong
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Tai-Juan Aw
- Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Melbourne, Australia
| | - Malcolm J Brown
- Department of Biochemistry and Pharmacology, University of Melbourne, Melbourne, Australia
| | - Andrew Garnham
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Collene H Steward
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Kate T Murphy
- Institute for Health and Sport, Victoria University, Melbourne, Australia.,Centre for Muscle Research, Department of Anatomy and Physiology, University of Melbourne, Parkville, Australia
| | - Kate A Carey
- School of Women's and Children's Health, University of New South Wales, Sydney, Australia
| | - James Leppik
- Institute for Health and Sport, Victoria University, Melbourne, Australia
| | - Steve F Fraser
- Institute of Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia
| | - David Cameron-Smith
- Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore
| | - Henry Krum
- Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Melbourne, Australia
| | - Rodney J Snow
- Institute of Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia
| | - Michael J McKenna
- Institute for Health and Sport, Victoria University, Melbourne, Australia
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Hostrup M, Cairns SP, Bangsbo J. Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance. Compr Physiol 2021; 11:1895-1959. [PMID: 34190344 DOI: 10.1002/cphy.c190024] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Exercise causes major shifts in multiple ions (e.g., K+ , Na+ , H+ , lactate- , Ca2+ , and Cl- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K+ , Na+ , and Ca2+ during fatiguing exercise, while changes in gradients for Cl- and Cl- conductance may exert either protective or detrimental effects on fatigue. Myocellular H+ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca2+ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na+ /K+ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K+ and Cl- , respectively via metabolic regulation of the ATP-sensitive K+ channel (KATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.
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Affiliation(s)
- Morten Hostrup
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Simeon Peter Cairns
- SPRINZ, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.,Health and Rehabilitation Research Institute, Auckland University of Technology, Auckland, New Zealand
| | - Jens Bangsbo
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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The role of AMPK in regulation of Na +,K +-ATPase in skeletal muscle: does the gauge always plug the sink? J Muscle Res Cell Motil 2021; 42:77-97. [PMID: 33398789 DOI: 10.1007/s10974-020-09594-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 12/14/2020] [Indexed: 12/14/2022]
Abstract
AMP-activated protein kinase (AMPK) is a cellular energy gauge and a major regulator of cellular energy homeostasis. Once activated, AMPK stimulates nutrient uptake and the ATP-producing catabolic pathways, while it suppresses the ATP-consuming anabolic pathways, thus helping to maintain the cellular energy balance under energy-deprived conditions. As much as ~ 20-25% of the whole-body ATP consumption occurs due to a reaction catalysed by Na+,K+-ATPase (NKA). Being the single most important sink of energy, NKA might seem to be an essential target of the AMPK-mediated energy saving measures, yet NKA is vital for maintenance of transmembrane Na+ and K+ gradients, water homeostasis, cellular excitability, and the Na+-coupled transport of nutrients and ions. Consistent with the model that AMPK regulates ATP consumption by NKA, activation of AMPK in the lung alveolar cells stimulates endocytosis of NKA, thus suppressing the transepithelial ion transport and the absorption of the alveolar fluid. In skeletal muscles, contractions activate NKA, which opposes a rundown of transmembrane ion gradients, as well as AMPK, which plays an important role in adaptations to exercise. Inhibition of NKA in contracting skeletal muscle accentuates perturbations in ion concentrations and accelerates development of fatigue. However, different models suggest that AMPK does not inhibit or even stimulates NKA in skeletal muscle, which appears to contradict the idea that AMPK maintains the cellular energy balance by always suppressing ATP-consuming processes. In this short review, we examine the role of AMPK in regulation of NKA in skeletal muscle and discuss the apparent paradox of AMPK-stimulated ATP consumption.
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Pirkmajer S, Chibalin AV. Na,K-ATPase regulation in skeletal muscle. Am J Physiol Endocrinol Metab 2016; 311:E1-E31. [PMID: 27166285 DOI: 10.1152/ajpendo.00539.2015] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Accepted: 05/02/2016] [Indexed: 12/17/2022]
Abstract
Skeletal muscle contains one of the largest and the most dynamic pools of Na,K-ATPase (NKA) in the body. Under resting conditions, NKA in skeletal muscle operates at only a fraction of maximal pumping capacity, but it can be markedly activated when demands for ion transport increase, such as during exercise or following food intake. Given the size, capacity, and dynamic range of the NKA pool in skeletal muscle, its tight regulation is essential to maintain whole body homeostasis as well as muscle function. To reconcile functional needs of systemic homeostasis with those of skeletal muscle, NKA is regulated in a coordinated manner by extrinsic stimuli, such as hormones and nerve-derived factors, as well as by local stimuli arising in skeletal muscle fibers, such as contractions and muscle energy status. These stimuli regulate NKA acutely by controlling its enzymatic activity and/or its distribution between the plasma membrane and the intracellular storage compartment. They also regulate NKA chronically by controlling NKA gene expression, thus determining total NKA content in skeletal muscle and its maximal pumping capacity. This review focuses on molecular mechanisms that underlie regulation of NKA in skeletal muscle by major extrinsic and local stimuli. Special emphasis is given to stimuli and mechanisms linking regulation of NKA and energy metabolism in skeletal muscle, such as insulin and the energy-sensing AMP-activated protein kinase. Finally, the recently uncovered roles for glutathionylation, nitric oxide, and extracellular K(+) in the regulation of NKA in skeletal muscle are highlighted.
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Affiliation(s)
- Sergej Pirkmajer
- Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia; and
| | - Alexander V Chibalin
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden
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5
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Benziane B, Björnholm M, Pirkmajer S, Austin RL, Kotova O, Viollet B, Zierath JR, Chibalin AV. Activation of AMP-activated protein kinase stimulates Na+,K+-ATPase activity in skeletal muscle cells. J Biol Chem 2012; 287:23451-63. [PMID: 22610379 DOI: 10.1074/jbc.m111.331926] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Contraction stimulates Na(+),K(+)-ATPase and AMP-activated protein kinase (AMPK) activity in skeletal muscle. Whether AMPK activation affects Na(+),K(+)-ATPase activity in skeletal muscle remains to be determined. Short term stimulation of rat L6 myotubes with the AMPK activator 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR), activates AMPK and promotes translocation of the Na(+),K(+)-ATPase α(1)-subunit to the plasma membrane and increases Na(+),K(+)-ATPase activity as assessed by ouabain-sensitive (86)Rb(+) uptake. Cyanide-induced artificial anoxia, as well as a direct AMPK activator (A-769662) also increase AMPK phosphorylation and Na(+),K(+)-ATPase activity. Thus, different stimuli that target AMPK concomitantly increase Na(+),K(+)-ATPase activity. The effect of AICAR on Na(+),K(+)-ATPase in L6 myotubes was attenuated by Compound C, an AMPK inhibitor, as well as siRNA-mediated AMPK silencing. The effects of AICAR on Na(+),K(+)-ATPase were completely abolished in cultured primary mouse muscle cells lacking AMPK α-subunits. AMPK stimulation leads to Na(+),K(+)-ATPase α(1)-subunit dephosphorylation at Ser(18), which may prevent endocytosis of the sodium pump. AICAR stimulation leads to methylation and dephosphorylation of the catalytic subunit of the protein phosphatase (PP) 2A in L6 myotubes. Moreover, AICAR-triggered dephosphorylation of the Na(+),K(+)-ATPase was prevented in L6 myotubes deficient in PP2A-specific protein phosphatase methylesterase-1 (PME-1), indicating a role for the PP2A·PME-1 complex in AMPK-mediated regulation of Na(+),K(+)-ATPase. Thus contrary to the common paradigm, we report AMPK-dependent activation of an energy-consuming ion pumping process. This activation may be a potential mechanism by which exercise and metabolic stress activate the sodium pump in skeletal muscle.
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Affiliation(s)
- Boubacar Benziane
- Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden
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Change Characteristics of Women boxers’ Na+,K+- ATPase, ROS and T-AOC before the Match. ACTA ACUST UNITED AC 2012. [DOI: 10.1016/j.egypro.2012.02.153] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Thomassen M, Rose AJ, Jensen TE, Maarbjerg SJ, Bune L, Leitges M, Richter EA, Bangsbo J, Nordsborg NB. Protein kinase Cα activity is important for contraction-induced FXYD1 phosphorylation in skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2011; 301:R1808-14. [DOI: 10.1152/ajpregu.00066.2011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Exercise-induced phosphorylation of FXYD1 is a potential important regulator of Na+-K+-pump activity. It was investigated whether skeletal muscle contractions induce phosphorylation of FXYD1 and whether protein kinase Cα (PKCα) activity is a prerequisite for this possible mechanism. In part 1, human muscle biopsies were obtained at rest, after 30 s of high-intensity exercise (166 ± 31% of V̇o2max) and after a subsequent 20 min of moderate-intensity exercise (79 ± 8% of V̇o2max). In general, FXYD1 phosphorylation was increased compared with rest both after 30 s ( P < 0.05) and 20 min ( P < 0.001), and more so after 20 min compared with 30 s ( P < 0.05). Specifically, FXYD1 ser63, ser68, and combined ser68 and thr69 phosphorylation were 26–45% higher ( P < 0.05) after 20 min of exercise than at rest. In part 2, FXYD1 phosphorylation was investigated in electrically stimulated soleus and EDL muscles from PKCα knockout (KO) and wild-type (WT) mice. Contractile activity caused FXYD1 ser68 phosphorylation to be increased ( P < 0.001) in WT soleus muscles but to be reduced ( P < 0.001) in WT extensor digitorum longus. In contrast, contractile activity did not affect FXYD1 ser68 phosphorylation in the KO mice. In conclusion, exercise induces FXYD1 phosphorylation at multiple sites in human skeletal muscle. In mouse muscles, contraction-induced changes in FXYD1 ser68 phosphorylation are fiber-type specific and dependent on PKCα activity.
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Affiliation(s)
- Martin Thomassen
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Adam J. Rose
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
- Division Molecular Metabolic Control, German Cancer Research Center, Heidelberg, Germany; and
| | - Thomas E. Jensen
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Stine J. Maarbjerg
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Laurids Bune
- Copenhagen Muscle Research Centre, Rigshospitalet, Denmark
| | - Michael Leitges
- The Biotechnology Centre of Oslo, University of Oslo, Blindern, Oslo, Norway
| | - Erik A. Richter
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens Bangsbo
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Nikolai B. Nordsborg
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
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Rose AJ, Jeppesen J, Kiens B, Richter EA. Effects of contraction on localization of GLUT4 and v-SNARE isoforms in rat skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2009; 297:R1228-37. [PMID: 19675279 DOI: 10.1152/ajpregu.00258.2009] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In skeletal muscle, contractions increase glucose uptake due to a translocation of GLUT4 glucose transporters from intracellular storage sites to the surface membrane. Vesicle-associated membrane proteins (VAMPs) are believed to play an important role in docking and fusion of the GLUT4 transporters at the surface membrane. However, knowledge about which VAMP isoforms colocalize with GLUT4 vesicles in mature skeletal muscle and whether they translocate during muscle contractions is incomplete. The aim of the present study was to further identify VAMP isoforms, which are associated with GLUT4 vesicles and examine which VAMP isoforms translocate to surface membranes in skeletal muscles undergoing contractions. VAMP2, VAMP3, VAMP5, and VAMP7 were enriched in immunoprecipitated GLUT4 vesicles. In response to 20 min of in situ contractions, there was a redistribution of GLUT4 (+64 +/- 13%), transferrin receptor (TfR; +75 +/- 22%), and insulin-regulated aminopeptidase (IRAP; +70 +/- 13%) to fractions enriched in heavy membranes away from low-density membranes (-32 +/- 7%; -18 +/- 12%; -33 +/- 9%; respectively), when compared with the resting contralateral muscle. Similarly, there was a redistribution of VAMP2 (+240 +/- 40%), VAMP5 (+79 +/- 9%), and VAMP7 (+79 +/- 29%), but not VAMP3, to fractions enriched in heavy membranes away from low-density membranes (-49 +/- 10%, -54 +/- 9%, -14 +/- 11%, respectively) in contracted vs. resting muscle. In summary, VAMP2, VAMP3, VAMP5, and VAMP7 coimmunoprecipitate with intracellular GLUT4 vesicles in muscle, and VAMP2, VAMP5, VAMP7, but not VAMP3, translocate to the cell surface membranes similar to GLUT4, TfR, and IRAP in response to muscle contractions. These findings suggest that VAMP2, VAMP5, and VAMP7 may be involved in translocation of GLUT4 during muscle contractions.
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Affiliation(s)
- Adam J Rose
- Molecular Physiology Group, Department of Exercise and Sport Sciences, Copenhagen, Denmark.
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van den Burg MMM, Eizema K, de Graaf-Roelfsema E, van Breda E, Wijnberg ID, van der Kolk JH, Everts ME. Effects of acute exercise and long-term exercise on total Na+,K+-ATPase content and Na+,K+-ATPase isoform expression profile in equine muscle. Am J Vet Res 2009; 70:895-901. [DOI: 10.2460/ajvr.70.7.895] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Rigoard P, Chaillou M, Fares M, Sottejeau Y, Giot JP, Honfo-Ga C, Rohan J, Lapierre F, Maixent JM. [Energetic applications: Na+/K+-ATPase and neuromuscular transmission]. Neurochirurgie 2009; 55 Suppl 1:S92-103. [PMID: 19230940 DOI: 10.1016/j.neuchi.2008.06.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Accepted: 06/05/2008] [Indexed: 11/29/2022]
Abstract
Na/K-ATPase electrogenic activity and its indispensable role in maintaining gradients suggest that the modifications in isoform distribution and the functioning of the sodium pump have a major influence on both the neuronal functions, including excitability, and motor efficiency. This article proposes to clarify the involvement of Na/K-ATPase in the transmission of nerve influx within the peripheral nerve and then in the genesis, the maintenance, and the physiology of muscle contraction by comparing the data found in the literature with our work on neuron and muscle characterization of Na/K-ATPase activity and isoforms.
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Affiliation(s)
- P Rigoard
- Service de neurochirurgie, CHU La Milétrie, 2, rue de La Milétrie, BP 577, 86021 Poitiers cedex, France.
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Juel C. Na+-K+-ATPase in rat skeletal muscle: muscle fiber-specific differences in exercise-induced changes in ion affinity and maximal activity. Am J Physiol Regul Integr Comp Physiol 2008; 296:R125-32. [PMID: 18987285 DOI: 10.1152/ajpregu.90760.2008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
It is unclear whether muscle activity reduces or increases Na(+)-K(+)-ATPase maximal in vitro activity in rat skeletal muscle, and it is not known whether muscle activity changes the Na(+)-K(+)-ATPase ion affinity. The present study uses quantification of ATP hydrolysis to characterize muscle fiber type-specific changes in Na(+)-K(+)-ATPase activity in sarcolemmal membranes and in total membranes obtained from control rats and after 30 min of treadmill running. ATPase activity was measured at Na(+) concentrations of 0-80 mM and K(+) concentrations of 0-10 mM. K(m) and V(max) values were obtained from a Hill plot. K(m) for Na(+) was higher (lower affinity) in total membranes of glycolytic muscle (extensor digitorum longus and white vastus lateralis), when compared with oxidative muscle (red gastrocnemius and soleus). Treadmill running induced a significant decrease in K(m) for Na(+) in total membranes of glycolytic muscle, which abolished the fiber-type difference in Na(+) affinity. K(m) for K(+) (in the presence of Na(+)) was not influenced by running. Running only increased the maximal in vitro activity (V(max)) in total membranes from soleus, whereas V(max) remained constant in the three other muscles tested. In conclusion, muscle activity induces fiber type-specific changes both in Na(+) affinity and maximal in vitro activity of the Na(+)-K(+)-ATPase. The underlying mechanisms may involve translocation of subunits and increased association between PLM units and the alphabeta complex. The changes in Na(+)-K(+)-ATPase ion affinity are expected to influence muscle ion balance during muscle contraction.
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Affiliation(s)
- Carsten Juel
- Dept. of Biology, Univ. of Copenhagen, August Krogh Bldg., Universitetsparken 13, DK-2100 Copenhagen, Denmark.
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Rasmussen MK, Kristensen M, Juel C. Exercise-induced regulation of phospholemman (FXYD1) in rat skeletal muscle: implications for Na+/K+-ATPase activity. Acta Physiol (Oxf) 2008; 194:67-79. [PMID: 18373741 DOI: 10.1111/j.1748-1716.2008.01857.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Na(+)/K(+)-ATPase activity is upregulated during muscle exercise to maintain ionic homeostasis. One mechanism may involve movement of alpha-subunits to the outer membrane (translocation). AIM We investigated the existence of exercise-induced translocation and phosphorylation of phospholemman (PLM, FXYD1) protein in rat skeletal muscle and exercise-induced changes in V(max) and K(m) for Na(+) of the Na(+)/K(+)-ATPase. METHODS Two membrane fractionation methods and immunoprecipitation were used. RESULTS Both fractionation methods revealed a 200-350% increase in PLM in the sarcolemma after 30 min of treadmill running, while the phosphorylation of Ser-68 of PLM appeared to be unchanged. Exercise did not change V(max) or K(m) for Na(+) of the Na(+)/K(+)-ATPase in muscle homogenate, but induced a 67% increase in V(max) in the sarcolemmal giant vesicle preparation; K(m) for Na(+) remained constant. The main part of the increase in V(max) is related to a 36-53% increase in the level of alpha-subunits; the remainder may be related to increased PLM content. Similar results were obtained with another membrane purification method. In resting muscle, 29% and 32% of alpha(1)- and alpha(2)-subunits, respectively, were co-immunoprecipitated by PLM antibodies. In muscle homogenate prepared after exercise, immunoprecipitation of alpha(1)-subunits was increased to 227%, whereas the fraction of precipitated alpha(2) remained constant. CONCLUSION Exercise translocates PLM to the muscle outer membrane and increases its association with mainly the alpha(1)-subunit, which may contribute to the increased V(max) of the Na(+)/K(+)-ATPase.
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Affiliation(s)
- M K Rasmussen
- Department of Molecular Biology, Copenhagen Muscle Research Centre, University of Copenhagen, Denmark
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Benziane B, Chibalin AV. Frontiers: skeletal muscle sodium pump regulation: a translocation paradigm. Am J Physiol Endocrinol Metab 2008; 295:E553-8. [PMID: 18430962 DOI: 10.1152/ajpendo.90261.2008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The skeletal muscle sodium pump plays a major role in the removal of K(+) ions from the circulation postprandial, or after a physical activity bout, thereby preventing the development of hyperkalemia and fatigue. Insulin and muscle contractions stimulate Na(+)-K(+)-ATPase activity in skeletal muscle, at least partially via translocation of sodium pump units to the plasma membrane from intracellular stores. The molecular mechanism of this phenomenon is poorly understood. Due to the contradictory reports in the literature, the very existence of the translocation of Na(+)-K(+)-ATPase to the skeletal muscle cell surface is questionable. This review summarizes more than 30 years work on the skeletal muscle sodium pump translocation paradigm. Furthermore, the methodological caveats of major approaches to study the sodium pump translocation in skeletal muscle are discussed. An understanding of the molecular regulation of Na(+)-K(+)-ATPase in skeletal muscle will have important clinical implications for the understanding of the development of complications associated with the metabolic syndrome, such as cardiovascular diseases or increased muscle fatigue in diabetic patients.
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Affiliation(s)
- Boubacar Benziane
- Deptartment of Molecular Medicine and Surgery, Integrative Physiology, Karolinska Institutet 171 77, Stockholm Sweden
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Iaia FM, Thomassen M, Kolding H, Gunnarsson T, Wendell J, Rostgaard T, Nordsborg N, Krustrup P, Nybo L, Hellsten Y, Bangsbo J. Reduced volume but increased training intensity elevates muscle Na+-K+ pump α1-subunit and NHE1 expression as well as short-term work capacity in humans. Am J Physiol Regul Integr Comp Physiol 2008; 294:R966-74. [DOI: 10.1152/ajpregu.00666.2007] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners after a change from endurance to sprint training. Fifteen runners were assigned to either a sprint training (ST, n = 8) or a control (CON, n = 7) group. ST replaced their normal training by 30-s sprint runs three to four times a week, whereas CON continued the endurance training (∼45 km/wk). After the 4-wk sprint period, the expression of the muscle Na+-K+ pump α1-subunit and Na+/H+-exchanger isoform 1 was 29 and 30% higher ( P < 0.05), respectively. Furthermore, plasma K+ concentration was reduced ( P < 0.05) during repeated intense running. In ST, performance in a 30-s sprint test, Yo-Yo intermittent recovery test, and two supramaximal exhaustive runs was improved ( P < 0.05) by 7, 19, 27, and 19%, respectively, after the sprint training period, whereas pulmonary maximum oxygen uptake and 10-k time were unchanged. No changes in CON were observed. The present data suggest a role of the Na+-K+ pump in the control of K+ homeostasis and in the development of fatigue during repeated high-intensity exercise. Furthermore, performance during intense exercise can be improved and endurance performance maintained even with a reduction in training volume if the intensity of training is very high.
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Na(+)-K (+) pump location and translocation during muscle contraction in rat skeletal muscle. Pflugers Arch 2008; 456:979-89. [PMID: 18214523 DOI: 10.1007/s00424-008-0449-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2007] [Revised: 01/07/2008] [Accepted: 01/09/2008] [Indexed: 10/22/2022]
Abstract
Muscle contraction may up-regulate the number of Na(+)-K(+) pumps in the plasma membrane by translocation of subunits. Since there is still controversy about where this translocation takes place from and if it takes place at all, the present study used different techniques to characterize the translocation. Electrical stimulation and biotin labeling of rat muscle revealed a 40% and 18% increase in the amounts of the Na(+)-K(+) pump alpha(2) subunit and caveolin-3 (Cav-3), respectively, in the sarcolemma. Exercise induced a 36% and 19% increase in the relative amounts of the alpha(2) subunit and Cav-3, respectively, in an outer-membrane-enriched fraction and a 41% and 17% increase, respectively, in sarcolemma giant vesicles. The Na(+)-K(+) pump activity measured with the 3-O-MFPase assay was increased by 37% in giant vesicles from exercised rats. Immunoprecipitation with Cav-3 antibody showed that 17%, 11% and 14% of the alpha(1) subunits were associated with Cav-3 in soleus, extensor digitorum longus, and mixed muscles, respectively. For the alpha(2), the corresponding values were 17%, 5% and 16%. In conclusion; muscle contraction induces translocation of the alpha subunits, which is suggested to be caused partly by structural changes in caveolae and partly by translocation from an intracellular pool.
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16
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Nordsborg N, Ovesen J, Thomassen M, Zangenberg M, Jøns C, Iaia FM, Nielsen JJ, Bangsbo J. Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans. J Physiol 2008; 586:1447-59. [PMID: 18174214 DOI: 10.1113/jphysiol.2007.143073] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The effect of dexamethasone on Na(+),K(+) pump subunit expression and muscle exchange of K(+) during exercise in humans was investigated. Nine healthy male subjects completed a randomized double blind placebo controlled protocol, with ingestion of dexamethasone (Dex: 2 x 2 mg per day) or placebo (Pla) for 5 days. Na(+),K(+) pump catalytic alpha1 and alpha2 subunit expression was approximately 17% higher (P < 0.05) and the structural beta1 and beta2 subunit expression was approximately 6-8% higher (P < 0.05) after Dex compared with Pla. During one-legged knee-extension for 10 min at low intensity (LI; 18.6 +/- 1.0 W), two moderate intensity (51.7 +/- 2.4 W) exercise bouts (MI(1): 5 min; 2 min recovery; MI(2): exhaustive) and two high-intensity (71.7 +/- 2.5 W) exercise bouts (HI(1): 1 min 40 s; 2 min recovery; HI(2): exhaustive), femoral venous K(+) was lower (P < 0.05) in Dex compared with Pla. Thigh K(+) release was lower (P < 0.05) in Dex compared with Pla in LI and MI, but not in HI. Time to exhaustion in MI(2) tended to improve (393 +/- 50 s versus 294 +/- 41 s; P = 0.07) in Dex compared with Pla, whereas no difference was detected in HI(2) (106 +/- 10 s versus 108 +/- 9 s). The results indicate that an increased Na(+),K(+) pump expression per se is of importance for thigh K(+) reuptake at the onset of low and moderate intensity exercise, but less important during high intensity exercise.
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Affiliation(s)
- Nikolai Nordsborg
- University of Copenhagen, Department of Exercise and Sport Sciences, Section for Human Physiology, Universitetsparken 13, 2100 Copenhagen, Denmark.
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17
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Green HJ, Duhamel TA, Holloway GP, Moule JW, Ouyang J, Ranney D, Tupling AR. Muscle Na+-K+-ATPase response during 16 h of heavy intermittent cycle exercise. Am J Physiol Endocrinol Metab 2007; 293:E523-30. [PMID: 17488808 DOI: 10.1152/ajpendo.00004.2007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated the effects of a 16-h protocol of heavy intermittent exercise on the intrinsic activity and protein and isoform content of skeletal muscle Na(+)-K(+)-ATPase. The protocol consisted of 6 min of exercise performed once per hour at approximately 91% peak aerobic power (Vo(2 peak)) with tissue sampling from vastus lateralis before (B) and immediately after repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). Eleven untrained volunteers with a Vo(2 peak) of 44.3 +/- 2.3 ml x kg(-1) x min(-1) participated in the study. Maximal Na(+)-K(+)-ATPase activity (V(max), in nmol x mg protein(-1) x h(-1)) as measured by the 3-O-methylfluorescein K(+)-stimulated phosphatase assay was reduced (P < 0.05) by approximately 15% with exercise regardless of the number of repetitions performed. In addition, V(max) at R9 and R16 was lower (P < 0.05) than at R1 and R2. Vanadate-facilitated [(3)H]ouabain determination of Na(+)-K(+)-ATPase content (maximum binding capacity, pmol/g wet wt), although unaltered by exercise, increased (P < 0.05) 8.3% by R9 with no further increase observed at R16. Assessment of relative changes in isoform abundance measured at B as determined by quantitative immunoblotting showed a 26% increase (P < 0.05) in the alpha(2)-isoform by R2 and a 29% increase in alpha(3) by R9. At R16, beta(3) was lower (P < 0.05) than at R2 and R9. No changes were observed in alpha(1), beta(1), or beta(2). It is concluded that repeated sessions of heavy exercise, although resulting in increases in the alpha(2)- and alpha(3)-isoforms and decreases in beta(3)-isoform, also result in depression in maximal catalytic activity.
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Affiliation(s)
- H J Green
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada.
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18
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Green HJ, Duhamel TA, Foley KP, Ouyang J, Smith IC, Stewart RD. Glucose supplements increase human muscle in vitro Na+-K+-ATPase activity during prolonged exercise. Am J Physiol Regul Integr Comp Physiol 2007; 293:R354-62. [PMID: 17409263 DOI: 10.1152/ajpregu.00701.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Regulation of maximal Na+-K+-ATPase activity in vastus lateralis muscle was investigated in response to prolonged exercise with (G) and without (NG) oral glucose supplements. Fifteen untrained volunteers (14 males and 1 female) with a peak aerobic power (V̇o2peak) of 44.8 ± 1.9 ml·kg−1·min−1; mean ± SE cycled at ∼57% V̇o2peak to fatigue during both NG (artificial sweeteners) and G (6.13 ± 0.09% glucose) in randomized order. Consumption of beverage began at 30 min and continued every 15 min until fatigue. Time to fatigue was increased ( P < 0.05) in G compared with NG (137 ± 7 vs. 115 ± 6 min). Maximal Na+-K+-ATPase activity (Vmax) as measured by the 3- O-methylfluorescein phosphatase assay (nmol·mg−1·h−1) was not different between conditions prior to exercise (85.2 ± 3.3 or 86.0 ± 3.9), at 30 min (91.4 ± 4.7 vs. 91.9 ± 4.1) and at fatigue (92.8 ± 4.3 vs. 100 ± 5.0) but was higher ( P < 0.05) in G at 90 min (86.7 ± 4.2 vs. 109 ± 4.1). Na+-K+-ATPase content (βmax) measured by the vanadate facilitated [3H]ouabain-binding technique (pmol/g wet wt) although elevated ( P < 0.05) by exercise (0<30, 90, and fatigue) was not different between NG and G. At 60 and 90 min of exercise, blood glucose was higher ( P < 0.05) in G compared with NG. The G condition also resulted in higher ( P < 0.05) serum insulin at similar time points to glucose and lower ( P < 0.05) plasma epinephrine and norepinephrine at 90 min of exercise and at fatigue. These results suggest that G results in an increase in Vmax by mechanisms that are unclear.
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Affiliation(s)
- H J Green
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada.
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19
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Mohr M, Krustrup P, Nielsen JJ, Nybo L, Rasmussen MK, Juel C, Bangsbo J. Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development. Am J Physiol Regul Integr Comp Physiol 2006; 292:R1594-602. [PMID: 17194727 DOI: 10.1152/ajpregu.00251.2006] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study examined the effect of two different intense exercise training regimens on skeletal muscle ion transport systems, performance, and metabolic response to exercise. Thirteen subjects performed either sprint training [ST; 6-s sprints (n = 6)], or speed endurance training [SET; 30-s runs approximately 130% Vo(2 max), n = 7]. Training in the SET group provoked higher (P < 0.05) plasma K(+) levels and muscle lactate/H(+) accumulation. Only in the SET group was the amount of the Na(+)/H(+) exchanger isoform 1 (31%) and Na(+)-K(+)-ATPase isoform alpha(2) (68%) elevated (P < 0.05) after training. Both groups had higher (P < 0.05) levels of Na(+)-K(+)-ATPase beta(1)-isoform and monocarboxylate transporter 1 (MCT1), but no change in MCT4 and Na(+)-K(+)-ATPase alpha(1)-isoform. Both groups had greater (P < 0.05) accumulation of lactate during exhaustive exercise and higher (P < 0.05) rates of muscle lactate decrease after exercise. The ST group improved (P < 0.05) sprint performance, whereas the SET group elevated (P < 0.05) performance during exhaustive continuous treadmill running. Improvement in the Yo-Yo intermittent recovery test was larger (P < 0.05) in the SET than ST group (29% vs. 10%). Only the SET group had a decrease (P < 0.05) in fatigue index during a repeated sprint test. In conclusion, turnover of lactate/H(+) and K(+) in muscle during exercise does affect the adaptations of some but not all related muscle ion transport proteins with training. Adaptations with training do have an effect on the metabolic response to exercise and specific improvement in work capacity.
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Affiliation(s)
- Magni Mohr
- Copenhagen Muscle Research Centre, Institute of Exercise and Sport Sciences, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
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20
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Zhang L, Morris KJ, Ng YC. Fiber type-specific immunostaining of the Na+,K+-ATPase subunit isoforms in skeletal muscle: age-associated differential changes. Biochim Biophys Acta Mol Basis Dis 2006; 1762:783-93. [PMID: 16979878 PMCID: PMC1761903 DOI: 10.1016/j.bbadis.2006.08.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2006] [Revised: 08/15/2006] [Accepted: 08/15/2006] [Indexed: 11/22/2022]
Abstract
The expression of the Na(+),K(+)-ATPase alpha and beta subunit isoforms in rat skeletal muscle and its age-associated changes have been shown to be muscle-type dependent. The cellular basis underlying these findings is not completely understood. In this study, we examined the expression of Na(+),K(+)-ATPase isoforms in individual fiber types and tested the hypothesis that, with age, the changes in the expression of the isoforms differ among individual fibers. We utilized immunohistochemical techniques to examine the expression of the subunit isoforms at the individual fiber levels. Immunofluorescence staining of the subunit isoforms in both white gastrocnemius (GW) and red gastrocnemius (GR) revealed a predominance of staining on the sarcolemmal membrane. Compared to the skeletal muscle of 6-month-old rats, there were substantial increases in the levels of alpha1, beta1, and beta3 subunit isoforms, and decreases in the levels of alpha2 and beta2 in 30-month-old rats. In addition, we found distinct patterns of staining for the alpha1, alpha2, beta1, and beta2 isoforms in tissue sections from young and aged rats. Muscle fiber-typing was performed to correlate the pattern of staining with specific fiber types. Staining for alpha1 and alpha2 isoforms in the skeletal muscle of young rats was generally evenly distributed among the fibers of GW and GR, with the exception of higher alpha1 levels in slow-twitch oxidative Type I fibers of GR. By contrast, staining for the beta1 and beta2 isoforms in the mostly oxidative fibers and the mostly glycolytic fibers, respectively, was almost mutually exclusive. With age, there was a fiber-type selective qualitative decrease of alpha2 and beta2 in Type IIB fibers, and increase of beta1 in Type IIB fibers and beta2 in Type IID fibers of white gastrocnemius. These results provide, at the individual fiber level, a cellular basis for the differential expression of the Na(+),K(+)-ATPase subunit isoforms in the muscle groups. The data further indicate that the aged-associated changes in expression of the subunit isoforms occur in both a fiber-type specific as well as an across fiber-type manner. Because of the differing biochemical properties of the subunit isoforms, these changes add another layer of complexity in our understanding of the adaptation of the Na-pump in skeletal muscle with advancing age.
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Affiliation(s)
- Lianqin Zhang
- Department of Pharmacology, The Milton S. Hershey Medical Center, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania 17033
| | - Keith J. Morris
- Cell Biology Division, Institute of Ophthalmology, University College London, London, United Kingdom, EC1V 9EL
| | - Yuk-Chow Ng
- Department of Pharmacology, The Milton S. Hershey Medical Center, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania 17033
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21
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Yuan X, Luo S, Lin Z, Wu Y. Cyclic stretch translocates the alpha2-subunit of the Na pump to plasma membrane in skeletal muscle cells in vitro. Biochem Biophys Res Commun 2006; 348:750-7. [PMID: 16893515 DOI: 10.1016/j.bbrc.2006.07.120] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Accepted: 07/21/2006] [Indexed: 10/24/2022]
Abstract
The Na+-K+-ATPase and its regulation is important for maintaining membrane potential and transmembrane Na(+) gradient in all skeletal muscle cells and thus is essential for cell survival and function. In our previous study, cyclic stretch activated the Na pump in cultured skeletal muscle cells. Presently, we investigated whether this stimulation was the result of translocation of Na+-K+-ATPase from endosomes to the plasma membrane, and also evaluated the role of phosphatidylinositol 3-kinase (PI 3-kinase), the activation of which initiated vesicular trafficking and targeting of proteins to specific cell compartments. Skeletal muscle cells were stretched at 25% elongation continuous for 24h using the Flexercell Strain Unit. The plasma membrane and endosome fractions were isolated and Western blotted to localize the Na+-K+-ATPase alpha1- and alpha2-subunit protein. The results showed stretch increased Na+-K+-ATPase alpha1- and alpha2-subunit protein expression in plasma membrane fractions and decreased it in endosomes. The alpha2-subunit had a more dynamic response to mechanical stretch. PI 3-kinase inhibitors (LY294002) blocked the stretch-induced translocation of the Na+-K+-ATPase alpha2-subunit, while LY294002 had no effect on the transfer of alpha1-subunit. We concluded that cyclic stretch mainly stimulated the translocation of the alpha2-subunit of Na+-K+-ATPase from endosomes to the plasma membrane via a PI 3-kinase-dependent mechanism in cultured skeletal muscle cells in vitro, which in turn increased the activity of the Na pump.
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Affiliation(s)
- Xiao Yuan
- Department of Orthodontics, The 4th Military Medical University, Xi'an, Shanxi Province 710032, People's Republic of China.
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22
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Murphy KT, Petersen AC, Goodman C, Gong X, Leppik JA, Garnham AP, Cameron-Smith D, Snow RJ, McKenna MJ. Prolonged submaximal exercise induces isoform-specific Na+-K+-ATPase mRNA and protein responses in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2006; 290:R414-24. [PMID: 16179492 DOI: 10.1152/ajpregu.00172.2005] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated effects of prolonged submaximal exercise on Na+-K+-ATPase mRNA and protein expression, maximal activity, and content in human skeletal muscle. We also investigated the effects on mRNA expression of the transcription initiator gene, RNA polymerase II (RNAP II), and key genes involved in protein translation, eukaryotic initiation factor-4E (eIF-4E) and 4E-binding protein 1 (4E-BP1). Eleven subjects (6 men, 5 women) cycled at 75.5% (SD 4.8%) peak O2uptake and continued until fatigue. A vastus lateralis muscle biopsy was taken at rest, fatigue, and 3 and 24 h postexercise. We analyzed muscle for Na+-K+-ATPase α1, α2, α3, β1, β2, and β3, as well for RNAP II, eIF-4E, and 4E-BP1 mRNA expression by real-time RT-PCR and Na+-K+-ATPase isoform protein abundance using immunoblotting. Muscle homogenate maximal Na+-K+-ATPase activity was determined by 3 -O-methylfluorescein phosphatase activity and Na+-K+-ATPase content by [3H]ouabain binding. Cycling to fatigue [54.5 (SD 20.6) min] immediately increased α3( P = 0.044) and β2mRNA ( P = 0.042) by 2.2- and 1.9-fold, respectively, whereas α1mRNA was elevated by 2.0-fold at 24 h postexercise ( P = 0.036). A significant time main effect was found for α3protein abundance ( P = 0.046). Exercise transiently depressed maximal Na+-K+-ATPase activity ( P = 0.004), but Na+-K+-ATPase content was unaltered throughout recovery. Exercise immediately increased RNAP II mRNA by 2.6-fold ( P = 0.011) but had no effect on eIF-4E and 4E-BP1 mRNA. Thus a single bout of prolonged submaximal exercise induced isoform-specific Na+-K+-ATPase responses, increasing α1, α3, and β2mRNA but only α3protein expression. Exercise also increased mRNA expression of RNAP II, a gene initiating transcription, but not of eIF-4E and 4E-BP1, key genes initiating protein translation.
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Affiliation(s)
- K T Murphy
- Muscle, Ions, and Exercise Group, School of Human Movement, Recreation and Performance, Victoria University of Technology, Melbourne, Victoria, Australia
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23
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Sandiford SDE, Green HJ, Ouyang J. Mechanisms underlying increases in rat soleus Na+-K+-ATPase activity by induced contractions. J Appl Physiol (1985) 2005; 99:2222-32. [PMID: 16109830 DOI: 10.1152/japplphysiol.00577.2005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Acute regulation of the Na(+)-K(+)-ATPase activity in rat soleus muscle was investigated in response to 15 and 90 min of electrically induced contractile activity (500-ms trains at 30 Hz every 1.5 s). Kinetic measurements of Na(+)-K(+)-ATPase activity, assessed by the 3-O-methylfluorescein K(+)-stimulated phosphatase assay (3-O-MFP), were performed on crude homogenates (Hom) and on tissue separated into two membrane fractions, the sarcolemmal/particulate (SLP) and endosomal (En), in both stimulated (Stim) and contralateral control (Con) muscles. Maximal 3-O-MFP activity (V(max), nmol.mg protein(-1).h(-1)) was elevated (P < 0.05) in Stim by 40% and by 53% in Hom and by 37 and 40% in SLP at 15 and 90 min, respectively. The 38% increase (P < 0.05) in the alpha(2)-isoform subunit distribution in SLP at 15 min, as assessed by quantitative immunoblotting, persisted at 90 min, whereas for En a 42% decrease (P < 0.05) was observed only at 15 min. For the alpha(1)-subunit at 15 min, a 27% decrease (P < 0.05) was observed in En, whereas the 13% increase observed in SLP was not significant (P = 0.08). At 90 min, alpha(1) was increased (P < 0.05) by 14% in SLP and by 29% in En. No changes were observed in beta(1)-subunit distribution in En and SLP regardless of time of stimulation. Immunoprecipitation with antiphosphotyrosine antibody and quantitative immunoblotting with alpha(1)- and alpha(2)-antibodies indicated increases (P < 0.05) in tyrosine phosphorylation of 51% in alpha(2) at 15 min only. These results suggest that the increases in V(max) during contractile activity are mediated both by increased phosphorylation and by translocation of the enzyme to the plasma membrane.
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Affiliation(s)
- S D E Sandiford
- Dept. of Kinesiology, University of Waterloo, Waterloo, ON, Canada
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24
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Roy BD, de Beer J, Harvey D, Tarnopolsky MA. Creatine Monohydrate Supplementation Does Not Improve Functional Recovery After Total Knee Arthroplasty. Arch Phys Med Rehabil 2005; 86:1293-8. [PMID: 16003653 DOI: 10.1016/j.apmr.2005.01.005] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
OBJECTIVE To determine if creatine monohydrate supplementation can improve body composition and enhance recovery after total knee arthroplasty (TKA). DESIGN Randomized trial in which creatine monohydrate or placebo was administered. SETTING Public primary care facility. PARTICIPANTS Thirty-seven adults (17 men, 20 women) with osteoarthritis undergoing TKA. Intervention Subjects received creatine monohydrate (10 g/d x 10 d presurgery to 5 g/d x 30 d postsurgery) or placebo. MAIN OUTCOME MEASURES Body composition (dual-energy x-ray absorptiometry scanning), muscle metabolite concentrations (adenosine triphosphate, phosphocreatine, creatine, total creatine [phosphocreatine + creatine]), muscle histomorphometery, quadriceps, ankle dorsiflexion and handgrip strength, and functional capacity. All measurements were completed preoperatively (-7 d) and 30 days postoperatively, except for that of muscle metabolites. Muscle metabolite samples were collected during surgery (0 d) and at 30 days. RESULTS A significant decrease in quadriceps and ankle dorsiflexion strength was observed at 30 days postoperatively (P < .01). There were no significant effects of creatine monohydrate supplementation on any of the measured outcome variables. CONCLUSIONS Creatine monohydrate supplementation did not improve body composition or muscle strength when given before surgery, nor did it enhance recovery after TKA.
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Affiliation(s)
- Brian D Roy
- Faculty of Applied Health Sciences, Brock University, St. Catharines, ON, Canada
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25
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Petersen AC, Murphy KT, Snow RJ, Leppik JA, Aughey RJ, Garnham AP, Cameron-Smith D, McKenna MJ. Depressed Na+-K+-ATPase activity in skeletal muscle at fatigue is correlated with increased Na+-K+-ATPase mRNA expression following intense exercise. Am J Physiol Regul Integr Comp Physiol 2005; 289:R266-74. [PMID: 15790751 DOI: 10.1152/ajpregu.00378.2004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated whether depressed muscle Na+-K+-ATPase activity with exercise reflected a loss of Na+-K+-ATPase units, the time course of its recovery postexercise, and whether this depressed activity was related to increased Na+-K+-ATPase isoform gene expression. Fifteen subjects performed fatiguing, knee extensor exercise at ∼40% maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue, 3 h, and 24 h postexercise and analyzed for maximal Na+-K+-ATPase activity via 3- O-methylfluorescein phosphatase (3- O-MFPase) activity, Na+-K+-ATPase content via [3H]ouabain binding sites, and Na+-K+-ATPase α1-, α2-, α3-, β1-, β2- and β3-isoform mRNA expression by real-time RT-PCR. Exercise [352 (SD 267) s] did not affect [3H]ouabain binding sites but decreased 3- O-MFPase activity by 10.7 (SD 8)% ( P < 0.05), which had recovered by 3 h postexercise, without further change at 24 h. Exercise elevated α1-isoform mRNA by 1.5-fold at fatigue ( P < 0.05). This increase was inversely correlated with the percent change in 3- O-MFPase activity from rest to fatigue (%Δ3- O-MFPaserest-fatigue) ( r = −0.60, P < 0.05). The average postexercise (fatigue, 3 h, 24 h) α1-isoform mRNA was increased 1.4-fold ( P < 0.05) and approached a significant inverse correlation with %Δ3- O-MFPaserest-fatigue( r = −0.56, P = 0.08). Exercise elevated α2-isoform mRNA at fatigue 2.5-fold ( P < 0.05), which was inversely correlated with %Δ3- O-MFPaserest-fatigue( r = −0.60, P = 0.05). The average postexercise α2-isoform mRNA was increased 2.2-fold ( P < 0.05) and was inversely correlated with the %Δ3- O-MFPaserest-fatigue( r = −0.68, P < 0.05). Nonsignificant correlations were found between %Δ3- O-MFPaserest-fatigueand other isoforms. Thus acute exercise transiently decreased Na+-K+-ATPase activity, which was correlated with increased Na+-K+-ATPase gene expression. This suggests a possible signal-transduction role for depressed muscle Na+-K+-ATPase activity with exercise.
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Affiliation(s)
- A C Petersen
- Muscle, Ions and Exercise Group, School of Human Movement, Recreation and Performance, Centre for Ageing, Rehabilitation, Exercise, and Sport, Victoria University of Technology, PO Box 14428, MCMC, Melbourne, Victoria, Australia 8001
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26
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Nordsborg N, Thomassen M, Lundby C, Pilegaard H, Bangsbo J. Contraction-induced increases in Na+-K+-ATPase mRNA levels in human skeletal muscle are not amplified by activation of additional muscle mass. Am J Physiol Regul Integr Comp Physiol 2005; 289:R84-91. [PMID: 15705803 DOI: 10.1152/ajpregu.00771.2004] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study tested the hypothesis that exercise with a large compared with a small active muscle mass results in a higher contraction-induced increase in Na(+)-K(+)-ATPase mRNA expression due to greater hormonal responses. Furthermore, the relative abundance of Na(+)-K(+)-ATPase subunit alpha(1), alpha(2), alpha(3), alpha(4), beta(1), beta(2), and beta(3) mRNA in human skeletal muscle was investigated. On two occasions, eight subjects performed one-legged knee extension exercise (L) or combined one-legged knee extension and bilateral arm cranking (AL) for 5.00, 4.25, 3.50, 2.75, and 2.00 min separated by 3 min of rest. Leg exercise power output was the same in AL and L, but heart rate at the end of each exercise interval was higher in AL compared with L. One minute after exercise, arm venous blood lactate was higher in AL than in L. A higher level of blood epinephrine and norepinephrine was evident 3 min after exercise in AL compared with L. Nevertheless, none of the exercise-induced increases in alpha(1), alpha(2), beta(1), and beta(3) mRNA expression levels were higher in AL compared with L. The most abundant Na(+)-K(+)-ATPase subunit at the mRNA level was beta(1), which was expressed 3.4 times than alpha(2). Expression of alpha(1), beta(2), and beta(3) was less than 5% of the alpha(2) expression, and no reliable detection of alpha(3) and alpha(4) was possible. In conclusion, activation of additional muscle mass does not result in a higher exercise-induced increase in Na(+)-K(+)-ATPase subunit-specific mRNA.
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Affiliation(s)
- Nikolai Nordsborg
- Institute of Exercise and Sport Sciences, University of Copenhagen, Denmark
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27
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Green HJ, Barr DJ, Fowles JR, Sandiford SD, Ouyang J. Malleability of human skeletal muscle Na+-K+-ATPase pump with short-term training. J Appl Physiol (1985) 2004; 97:143-8. [PMID: 15220317 DOI: 10.1152/japplphysiol.00559.2003] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To investigate the hypothesis that short-term submaximal training would result in changes in Na+-K+-ATPase content, activity, and isoform distribution in skeletal muscle, seven healthy, untrained men [peak aerobic power (peak oxygen consumption; V̇o2 peak) = 45.6 ml·kg−1·min−1 (SE 5.4)] cycled for 2 h/day at 60–65% V̇o2 peak for 6 days. Muscle tissue, sampled from the vastus lateralis before training (0 days) and after 3 and 6 days of training and analyzed for Na+-K+-ATPase content, as assessed by the vanadate facilitated [3H]ouabain-binding technique, was increased ( P < 0.05) at 3 days (294 ± 8.6 pmol/g wet wt) and 6 days (308 ± 15 pmol/g wet wt) of training compared with 0 days (272 ± 9.7 pmol/g wet wt). Maximal Na+-K+-ATPase activity as evaluated by the 3- O-methylfluorescein phosphatase assay was increased ( P < 0.05) by 6 days (53.4 ± 5.9 nmol·h−1·mg protein−1) but not by 3 days (35.9 ± 4.5 nmol·h−1·mg protein−1) compared with 0 days (37.8 ± 3.7 nmol·h−1·mg protein−1) of training. Relative isoform distribution, measured by Western blot techniques, indicated increases ( P < 0.05) in α2-content by 3 days and β1-content by 6 days of training. These results indicate that prolonged aerobic exercise represents a potent stimulus for the rapid adaptation of Na+-K+-ATPase content, isoform, and activity characteristics.
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Affiliation(s)
- H J Green
- Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
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Mohr M, Nordsborg N, Nielsen JJ, Pedersen LD, Fischer C, Krustrup P, Bangsbo J. Potassium kinetics in human muscle interstitium during repeated intense exercise in relation to fatigue. Pflugers Arch 2004; 448:452-6. [PMID: 15048574 DOI: 10.1007/s00424-004-1257-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2003] [Revised: 01/26/2004] [Accepted: 02/19/2004] [Indexed: 11/30/2022]
Abstract
Accumulation of K+ in skeletal muscle interstitium during intense exercise has been suggested to cause fatigue in humans. The present study examined interstitial K+ kinetics and fatigue during repeated, intense, exhaustive exercise in human skeletal muscle. Ten subjects performed three repeated, intense (61.6+/-4.1 W; mean+/-SEM), one-legged knee extension exercise bouts (EX1, EX2 and EX3) to exhaustion separated by 10-min recovery periods. Interstitial [K+] ([K+]interst) in the vastus lateralis muscle were determined using microdialysis. Time-to-fatigue decreased progressively (P<0.05) during the protocol (5.1+/-0.4, 4.2+/-0.3 and 3.2+/-0.2 min for EX1, EX2 and EX3 respectively). Prior to these bouts, [K+]interst was 4.1+/-0.2, 4.8+/-0.2 and 5.2+/-0.2 mM, respectively. During the initial 1.5 min of exercise the accumulation rate of interstitial K+ was 85% greater (P<0.05) in EX1 than in EX3. At exhaustion [K+]interst was 11.4+/-0.8 mM in EX1, which was not different from that in EX2 (10.4+/-0.8 mM), but higher (P<0.05) than in EX3 (9.1+/-0.3 mM). The study demonstrated that the rate of accumulation of K+ in the muscle interstitium declines during intense repetitive exercise. Furthermore, whilst [K+]interst at exhaustion reached levels high enough to impair performance, the concentration decreased with repeated exercise, suggesting that accumulation of interstitial K+ per se does not cause fatigue when intense exercise is repeated.
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Affiliation(s)
- Magni Mohr
- Institute of Exercise and Sport Sciences, Department of Human Physiology, August Krogh Institute, University of Copenhagen, Universitetsparken 13, 2100, Copenhagen Ø, Denmark
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Bickham DC. Extracellular K+ accumulation: a physiological framework for fatigue during intense exercise. J Physiol 2004; 554:593. [PMID: 14673181 PMCID: PMC1664804 DOI: 10.1113/jphysiol.2003.059139] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Affiliation(s)
- Dale C Bickham
- Biological Structure and Function Section, Division of Biomedical Sciences, Imperial College, South Kensington, London SW8 2AZ, UK.
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Nielsen JJ, Mohr M, Klarskov C, Kristensen M, Krustrup P, Juel C, Bangsbo J. Effects of high-intensity intermittent training on potassium kinetics and performance in human skeletal muscle. J Physiol 2004; 554:857-70. [PMID: 14634198 PMCID: PMC1664795 DOI: 10.1113/jphysiol.2003.050658] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2003] [Accepted: 11/21/2003] [Indexed: 12/29/2022] Open
Abstract
A rise in extracellular potassium concentration in human skeletal muscle may play an important role in development of fatigue during intense exercise. The aim of the present study was to examine the effect of intense intermittent training on muscle interstitial potassium kinetics and its relationship to the density of Na(+),K(+)-ATPase subunits and K(ATP) channels, as well as exercise performance, in human skeletal muscle. Six male subjects performed intense one-legged knee-extensor training for 7 weeks. On separate days the trained leg (TL) and the control leg (CL) performed a 30 min exercise period of 30 W and an incremental test to exhaustion. At frequent intervals during the exercise periods interstitial potassium ([K(+)](I)) was determined by microdialysis, femoral arterial and venous blood samples were drawn and thigh blood flow was measured. Time to fatigue for TL was 28% longer (P < 0.05) than for CL (10.6 +/- 0.7 (mean +/-s.e.m.) versus 8.2 +/- 0.7 min). The amounts of Na(+),K(+)-ATPase alpha(1) and alpha(2) subunits were, respectively, 29.0 +/- 8.4 and 15.1 +/- 2.7% higher (P < 0.05) in TL than in CL, while the amounts of beta(1) subunits and ATP-dependent K(+) (K(ATP)) channels were the same. In CL [K(+)](I) increased more rapidly and was higher (P < 0.05) throughout the 30 W exercise bout, as well at 60 and 70 W, compared to TL, whereas [K(+)](I) was similar at the point of fatigue (9.9 +/- 0.7 and 9.1 +/- 0.5 mmol l(-1), respectively). During the 30 W exercise bouts and at 70 W during the incremental exercise femoral venous potassium concentration ([K(+)](v)) was higher (P < 0.05) in CL than in TL, but identical at exhaustion (6.2 +/- 0.2 mmol l(-1)). Release of potassium to the blood was not different in the two legs. The present data demonstrated that intense intermittent training reduce accumulation of potassium in human skeletal muscle interstitium during exercise, probably through a larger re-uptake of potassium due to greater activity of the muscle Na(+),K(+)-ATPase pumps. The lower accumulation of potassium in muscle interstitium in the trained leg was associated with delayed fatigue during intense exercise, supporting the hypothesis that interstitial potassium accumulation is involved in the development of fatigue.
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Affiliation(s)
- Jens Jung Nielsen
- August Krogh Institute, IFI, Universitetsparken 13, DK-2100 Copenhagen Ø, Denmark
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Murphy KT, Snow RJ, Petersen AC, Murphy RM, Mollica J, Lee JS, Garnham AP, Aughey RJ, Leppik JA, Medved I, Cameron-Smith D, McKenna MJ. Intense exercise up-regulates Na+,K+-ATPase isoform mRNA, but not protein expression in human skeletal muscle. J Physiol 2004; 556:507-19. [PMID: 14754991 PMCID: PMC1664937 DOI: 10.1113/jphysiol.2003.054981] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Characterization of expression of, and consequently also the acute exercise effects on, Na(+),K(+)-ATPase isoforms in human skeletal muscle remains incomplete and was therefore investigated. Fifteen healthy subjects (eight males, seven females) performed fatiguing, knee extensor exercise at approximately 40% of their maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue and 3 and 24 h postexercise, and analysed for Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) mRNA and crude homogenate protein expression, using Real-Time RT-PCR and immunoblotting, respectively. Each individual expressed gene transcripts and protein bands for each Na(+),K(+)-ATPase isoform. Each isoform was also expressed in a primary human skeletal muscle cell culture. Intense exercise (352 +/- 69 s; mean +/-s.e.m.) immediately increased alpha(3) and beta(2) mRNA by 2.4- and 1.7-fold, respectively (P < 0.05), whilst alpha(1) and alpha(2) mRNA were increased by 2.5- and 3.5-fold at 24 h and 3 h postexercise, respectively (P < 0.05). No significant change occurred for beta(1) and beta(3) mRNA, reflecting variable time-dependent responses. When the average postexercise value was contrasted to rest, mRNA increased for alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, by 1.4-, 2.2-, 1.4-, 1.1-, 1.0- and 1.0-fold, respectively (P < 0.05). However, exercise did not alter the protein abundance of the alpha(1)-alpha(3) and beta(1)-beta(3) isoforms. Thus, human skeletal muscle expresses each of the Na(+),K(+)-ATPase alpha(1), alpha(2), alpha(3), beta(1), beta(2) and beta(3) isoforms, evidenced at both transcription and protein levels. Whilst brief exercise increased Na(+),K(+)-ATPase isoform mRNA expression, there was no effect on isoform protein expression, suggesting that the exercise challenge was insufficient for muscle Na(+),K(+)-ATPase up-regulation.
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Affiliation(s)
- K T Murphy
- School of Human Movement, Recreation and Performance (FO22), Victoria University of Technology, PO Box 14428, MCMC, Melbourne, Victoria, Australia
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Fowles JR, Green HJ, Ouyang J. Na+-K+-ATPase in rat skeletal muscle: content, isoform, and activity characteristics. J Appl Physiol (1985) 2004; 96:316-26. [PMID: 12882989 DOI: 10.1152/japplphysiol.00745.2002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of this study was to investigate the hypothesis that muscle Na+-K+-ATPase activity is directly related to Na+-K+-ATPase content and the content of the alpha2-catalytic isoform in muscles of different fiber-type composition. To investigate this hypothesis, tissue was sampled from soleus (Sol), red gastrocnemius (RG), white gastrocnemius (WG), and extensor digitorum longus (EDL) muscles at rest from 38 male Wistar rats weighing 413 +/- 6.0 g (mean +/- SE). Na+-K+-ATPase activity was determined in homogenates (Hom) and isolated crude membranes (CM) by the regenerating ouabain-inhibitable hydrolytic activity assay (ATPase) and the 3-O-methylfluorescein K+-stimulated phosphatase (3-O-MFPase) assay in vitro. In addition, Na+-K+-ATPase content (Bmax) and the distribution of alpha1-, alpha2-, beta1-, and beta2-isoforms were determined by [3H]ouabain binding and Western blot, respectively. For the ATPase assay, differences (P < 0.05) in enzyme activity between muscles were observed in Hom (EDL > WG) and in CM (Sol > EDL = WG). For the 3-O-MFPase assay, differences (P < 0.05) were also found for Hom (Sol > RG = EDL > WG) and CM (Sol = WG > RG). For Bmax, differences in the order of RG = EDL > Sol = WG (P < 0.05) were observed. Isoform distribution was similar between Hom and CM and indicated in CM, a greater density (P < 0.05) of alpha1 in Sol than WG and EDL (P < 0.05), but more equal distribution of alpha2 between muscles. The beta1 was greater (P < 0.05) in Sol and RG, and the beta2 was greater in EDL and WG (P < 0.05). Over all muscles, the correlation (r) between Hom 3-O-MFPase and Bmax was 0.45 (P < 0.05) and between Hom alpha2 and Bmax, 0.59 (P < 0.05). The alpha1 distribution correlated to Hom 3-O-MFPase (r = 0.79, P < 0.05) CM ATPase (r = 0.69, P < 0.005) and CM 3-O-MFPase activity (r = 0.32, P < 0.05). The alpha2 distribution was not correlated with any of the Na+-K+-ATPase activity measurements. The results indicate generally poor relationships between activity and total pump content and alpha2 isoform content of the Na+-K+-ATPase. Several factors, including the type of preparation and the type of assay, appear important in this regard.
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Affiliation(s)
- J R Fowles
- Deparment of Kinesiology, Univ. of Waterloo, Waterloo, ON, Canada N2L 3G1
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Abstract
Clausen, Torben. Na+-K+ Pump Regulation and Skeletal Muscle Contractility. Physiol Rev 83: 1269-1324, 2003; 10.1152/physrev.00011.2003.—In skeletal muscle, excitation may cause loss of K+, increased extracellular K+ ([K+]o), intracellular Na+ ([Na+]i), and depolarization. Since these events interfere with excitability, the processes of excitation can be self-limiting. During work, therefore, the impending loss of excitability has to be counterbalanced by prompt restoration of Na+-K+ gradients. Since this is the major function of the Na+-K+ pumps, it is crucial that their activity and capacity are adequate. This is achieved in two ways: 1) by acute activation of the Na+-K+ pumps and 2) by long-term regulation of Na+-K+ pump content or capacity. 1) Depending on frequency of stimulation, excitation may activate up to all of the Na+-K+ pumps available within 10 s, causing up to 22-fold increase in Na+ efflux. Activation of the Na+-K+ pumps by hormones is slower and less pronounced. When muscles are inhibited by high [K+]o or low [Na+]o, acute hormone- or excitation-induced activation of the Na+-K+ pumps can restore excitability and contractile force in 10-20 min. Conversely, inhibition of the Na+-K+ pumps by ouabain leads to progressive loss of contractility and endurance. 2) Na+-K+ pump content is upregulated by training, thyroid hormones, insulin, glucocorticoids, and K+ overload. Downregulation is seen during immobilization, K+ deficiency, hypoxia, heart failure, hypothyroidism, starvation, diabetes, alcoholism, myotonic dystrophy, and McArdle disease. Reduced Na+-K+ pump content leads to loss of contractility and endurance, possibly contributing to the fatigue associated with several of these conditions. Increasing excitation-induced Na+ influx by augmenting the open-time or the content of Na+ channels reduces contractile endurance. Excitability and contractility depend on the ratio between passive Na+-K+ leaks and Na+-K+ pump activity, the passive leaks often playing a dominant role. The Na+-K+ pump is a central target for regulation of Na+-K+ distribution and excitability, essential for second-to-second ongoing maintenance of excitability during work.
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Affiliation(s)
- Torben Clausen
- Department of Physiology, University of Aarhus, Arhus, Denmark.
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Ng YC, Nagarajan M, Jew KN, Mace LC, Moore RL. Exercise training differentially modifies age-associated alteration in expression of Na+-K+-ATPase subunit isoforms in rat skeletal muscles. Am J Physiol Regul Integr Comp Physiol 2003; 285:R733-40. [PMID: 12805093 DOI: 10.1152/ajpregu.00266.2003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study tests the hypothesis that endurance exercise training (ETr) reverses age-associated alterations in expression of Na+-K+-ATPase subunit isoforms in rat skeletal muscles. Expression of the isoforms was examined in 16-mo-old sedentary middle-aged, 29-mo-old sedentary senescent, and 29-mo-old treadmill exercise-trained senescent Fischer 344 x Brown Norway rats. Levels of the alpha1-isoform increased with age in red gastrocnemius (GR), white gastrocnemius (GW), and extensor digitorum longus (EDL) muscles, and ETr further increased its levels. Levels of the alpha2-isoform were unchanged in GR, had a strong trend for a decrease in GW, and decreased significantly in EDL. ETr increased expression of the alpha2-isoform in all three muscle groups. There was no increase in expression of the beta1-isoform in GR, GW, or EDL with age, whereas ETr markedly increased its levels in the muscles. There was a marked decrease with age in expression of the beta2-isoform in the muscle groups that was not reversed by ETr. By contrast, beta3-isoform levels increased with age in GR and GW, and ETr was able to reverse this increase. Na+-K+-ATPase enzyme activity was unchanged with age in GR and GW but increased in EDL. ETr increased enzyme activity in GR and GW and did not change in EDL. Myosin heavy chain isoforms in the muscle groups did not change significantly with age; ETr caused a general shift toward more oxidative fibers. Thus ETr differentially modifies age-associated alterations in expression of Na+-K+-ATPase subunit isoforms, and a mechanism(s) other than physical inactivity appears to play significant role in some of the age-associated changes.
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Affiliation(s)
- Yuk-Chow Ng
- Department of Pharmacology, Milton S Hershey Medical Center, The Pennsylvania State University, Hershey, Pennsylvania 17033, USA.
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35
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McKenna MJ, Gissel H, Clausen T. Effects of electrical stimulation and insulin on Na+-K+-ATPase ([3H]ouabain binding) in rat skeletal muscle. J Physiol 2003; 547:567-80. [PMID: 12562912 PMCID: PMC2342648 DOI: 10.1113/jphysiol.2003.034512] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Exercise has been reported to increase the Na+-K+-ATPase (Na+-K+ pump) alpha2 isoform in the plasma membrane 1.2- to 1.9-fold, purportedly reflecting Na+-K+ pump translocation from an undefined intracellular pool. We examined whether Na+-K+ pump stimulation, elicited by muscle contraction or insulin, increases the plasma membrane Na+-K+ pump content ([3H]ouabain binding) in muscles from young rats. Stimulation of isolated soleus muscle for 10 s at 120 Hz caused a rapid rise in intracellular Na+ content, followed by an 18-fold increase in the Na+ re-extrusion rate (80 % of theoretical maximum). Muscles frozen immediately or 120 s after 10-120 s stimulation showed 10-22 % decrease in [3H]ouabain binding expressed per gram wet weight, but with no significant change expressed per gram dry weight. In soleus muscles from adult rats, [3H]ouabain binding was unaltered after 10 s stimulation at 120 Hz. Extensor digitorum longus (EDL) muscles stimulated for 10-60 s at 120 Hz showed no significant change in [3H]ouabain binding. Insulin (100 mU ml-1) decreased intracellular Na+ content by 27 % and increased 86Rb uptake by 23 % soleus muscles, but [3H]ouabain binding was unchanged. After stimulation for 30 s at 60 Hz soleus muscle showed a 30% decrease in intracellular Na+ content, demonstrating increased Na+-K+ pump activity, but [3H]ouabain binding measured 5 to 120 min after stimulation was unchanged. Stimulation of soleus or EDL muscles for 120-240 min at 1 Hz (continuously) or 10 Hz (intermittently) produced no change in [3H]ouabain binding per gram dry weight. In conclusion, the stimulating effects of electrical stimulation or insulin on active Na+, K+-transport in rat skeletal muscle could not be even partially accounted for by an acute increase in the content of functional Na+ -K+ pumps in the plasma membrane.
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Affiliation(s)
- Michael J McKenna
- Department of Physiology, University of Aarhus, DK-8000 Arhus C., Denmark.
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Nielsen JJ, Kristensen M, Hellsten Y, Bangsbo J, Juel C. Localization and function of ATP-sensitive potassium channels in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol 2003; 284:R558-63. [PMID: 12388475 DOI: 10.1152/ajpregu.00303.2002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present study investigated the localization of ATP-sensitive K+ (KATP) channels in human skeletal muscle and the functional importance of these channels for human muscle K+ distribution at rest and during muscle activity. Membrane fractionation based on the giant vesicle technique or the sucrose-gradient technique in combination with Western blotting demonstrated that the KATP channels are mainly located in the sarcolemma. This localization was confirmed by immunohistochemical measurements. With the microdialysis technique, it was demonstrated that local application of the KATP channel inhibitor glibenclamide reduced (P < 0.05) interstitial K+ at rest from approximately 4.5 to 4.0 mM, whereas the concentration in the control leg remained constant. Glibenclamide had no effect on the interstitial K+ accumulation during knee-extensor exercise at a power output of 60 W. In contrast to in vitro conditions, the present study demonstrated that under in vivo conditions the KATP channels are active at rest and contribute to the accumulation of interstitial K+.
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Affiliation(s)
- Jens Jung Nielsen
- Copenhagen Muscle Research Centre, August Krogh Institute, and Institute of Exercise and Sports Sciences, Copenhagen, Denmark
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Buchanan R, Nielsen OB, Clausen T. Excitation- and beta(2)-agonist-induced activation of the Na(+)-K(+) pump in rat soleus muscle. J Physiol 2002; 545:229-40. [PMID: 12433963 PMCID: PMC2290663 DOI: 10.1113/jphysiol.2002.023325] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In rat skeletal muscle, Na(+)-K(+) pump activity increases dramatically in response to excitation (up to 20-fold) or beta(2)-agonists (2-fold), leading to a reduction in intracellular Na(+). This study examines the time course of these effects and whether they are due to an increased affinity of the Na(+)-K(+) pump for intracellular Na(+). Isolated rat soleus muscles were incubated at 30 (o)C in Krebs-Ringer bicarbonate buffer. The effects of direct electrical stimulation on (86)Rb(+) uptake rate and intracellular Na(+) concentration ([Na(+)](i)) were characterized in the subsequent recovery phase. [Na(+)](i) was varied using monensin or buffers with low Na(+). In the [Na(+)](i) range 21-69 mM, both the beta(2)-agonist salbutamol and electrical stimulation produced a left shift of the curves relating (86)Rb(+) uptake rate to [Na(+)](i). In the first 10 s after 1 or 10 s pulse trains of 60 Hz, [Na(+)](i) showed no increase, but (86)Rb(+) uptake rate increased by 22 and 86 %, respectively. Muscles excited in Na(+)-free Li(+)-substituted buffer and subsequently allowed to rest in standard buffer also showed a significant increase in (86)Rb(+) uptake rate and decrease in [Na(+)](i). Na(+) loading induced by monensin or electroporation also stimulated (86)Rb(+) uptake rate but, contrary to excitation, increased [Na(+)](i). The increase in the rate of (86)Rb(+) uptake elicited by electrical stimulation was abolished by ouabain, but not by bumetanide. The results indicate that excitation (like salbutamol) induces a rapid increase in the affinity of the Na(+)-K(+) pump for intracellular Na(+). This leads to a Na(+)-K(+) pump activation that does not require Na(+) influx, but possibly the generation of action potentials. This improves restoration of the Na(+)-K(+) homeostasis during work and optimizes excitability and contractile performance of the working muscle.
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Affiliation(s)
- Rasmus Buchanan
- Department of Physiology, University of Aarhus, DK-8000 Aarhus C, Denmark
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38
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Affiliation(s)
- Jurgen Schnermann
- National Institute of Diabetes and Digestive and Kidney Diseases/NIH, Bethesda, MD 20892, USA.
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39
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Overgaard K, Lindstrøm T, Ingemann-Hansen T, Clausen T. Membrane leakage and increased content of Na+ -K+ pumps and Ca2+ in human muscle after a 100-km run. J Appl Physiol (1985) 2002; 92:1891-8. [PMID: 11960939 DOI: 10.1152/japplphysiol.00669.2001] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During prolonged exercise, changes in the ionic milieu in and surrounding the muscle fibers may lead to fatigue or damage of the muscle and thereby impair performance. In 10 male subjects, we investigated the effects of 100 km running on muscle and plasma electrolyte contents, muscle Na+ -K+ pump content, and plasma concentrations of creatine kinase (CK) and lactate dehydrogenase (LDH). After completion of a 100-km run, significant increases were found in plasma K+ (from 4.0 +/- 0.1 to 5.5 +/- 0.2 mM, P < 0.001), muscle Na+ -K+ pump content (from 334 +/- 11 to 378 +/- 17 pmol/g, P < 0.05), and total muscle Ca2+ content (from 0.84 +/- 0.03 to 1.02 +/- 0.04 micromol/g, P < 0.001). There was also a large increase in the plasma levels of the muscle-specific enzymes CK and LDH, which reached peak values at the end of the run and lasted several days after the run, indicating that a significant degree of muscle membrane leakage was present. The simultaneous occurrence of raised cellular Ca2+ content and muscle membrane leakage supports the theory that Ca2+ plays a role in the initiation of degenerative processes in muscles after severe exercise.
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40
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Bryant NJ, Govers R, James DE. Regulated transport of the glucose transporter GLUT4. Nat Rev Mol Cell Biol 2002; 3:267-77. [PMID: 11994746 DOI: 10.1038/nrm782] [Citation(s) in RCA: 855] [Impact Index Per Article: 38.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In muscle and fat cells, insulin stimulates the delivery of the glucose transporter GLUT4 from an intracellular location to the cell surface, where it facilitates the reduction of plasma glucose levels. Understanding the molecular mechanisms that mediate this translocation event involves integrating our knowledge of two fundamental processes--the signal transduction pathways that are triggered when insulin binds to its receptor and the membrane transport events that need to be modified to divert GLUT4 from intracellular storage to an active plasma membrane shuttle service.
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Affiliation(s)
- Nia J Bryant
- Garvan Institute of Medical Research, 384 Victoria Road, Darlinghurst, New South Wales 2010, Australia
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41
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Fowles JR, Green HJ, Tupling R, O'Brien S, Roy BD. Human neuromuscular fatigue is associated with altered Na+-K+-ATPase activity following isometric exercise. J Appl Physiol (1985) 2002; 92:1585-93. [PMID: 11896025 DOI: 10.1152/japplphysiol.00668.2001] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The purpose of this study was to investigate the hypothesis that reductions in Na+-K+- ATPase activity are associated with neuromuscular fatigue following isometric exercise. In control (Con) and exercised (Ex) legs, force and electromyogram were measured in 14 volunteers [age, 23.4 +/- 0.7 (SE) yr] before and immediately after (PST0), 1 h after (PST1), and 4 h after (PST4) isometric, single-leg extension exercise at ~60% of maximal voluntary contraction for 30 min using a 0.5 duty cycle (5-s contraction, 5-s rest). Tissue was obtained from vastus lateralis muscle before exercise in Con and after exercise in both the Con (PST0) and Ex legs (PST0, PST1, PST4), for the measurements of Na+-K+-ATPase activity, as determined by the 3-O-methylfluorescein phosphatase (3-O-MFPase) assay. Voluntary (maximal voluntary contraction) and elicited (10, 20, 50, 100 Hz) force was reduced 30-55% (P < 0.05) at PST0 and did not recover by PST4. Muscle action potential (M-wave) amplitude and area (measured in the vastus medialis) and 3-O-MFPase activity at PST0-Ex were less than that at PST0-Con (P < 0.05) by 37, 25, and 38%, respectively. M-wave area at PST1-Ex was also less than that at PST1-Con (P < 0.05). Changes in 3-O-MFPase activity correlated to changes in M-wave area across all time points (r = 0.38, P < 0.05, n = 45). These results demonstrate that Na+-K+- ATPase activity is reduced by sustained isometric exercise in humans from that in a matched Con leg and that this reduction in Na+-K+-ATPase activity is associated with loss of excitability as indicated by M-wave alterations.
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Affiliation(s)
- J R Fowles
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
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Pestov NB, Korneenko TV, Zhao H, Adams G, Shakhparonov MI, Modyanov NN. Immunochemical demonstration of a novel beta-subunit isoform of X, K-ATPase in human skeletal muscle. Biochem Biophys Res Commun 2000; 277:430-5. [PMID: 11032740 DOI: 10.1006/bbrc.2000.3692] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recently we have identified mRNA encoding a hitherto unknown mammalian X,K-ATPase beta-subunit expressed predominantly in muscle tissue (Pestov, N. B. et al. (1999) FEBS Lett. 456, 243-248). Here we demonstrate the existence of the predicted protein, designated as beta(m) (beta(muscle)), in human adult skeletal muscle membranes using immunoblotting with beta(m)-specific antibodies generated against recombinant polypeptide formed by extramembrane beta(m) domains. The electrophoretic mobility of beta(m) was shown to be abnormally low due to the presence of Glu-rich sequences. In contrast to mature forms of other known X,K-ATPase beta-subunits, carbohydrate moiety of beta(m) is sensitive to endoglycosidase H and appears to be composed of short high-mannose or hybrid N-glycans. This finding argues in favor of an intracellular location of beta(m) in human skeletal muscle.
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Affiliation(s)
- N B Pestov
- Department of Pharmacology, Medical College of Ohio, Toledo, Ohio 43614, USA
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Sejersted OM, Sjøgaard G. Dynamics and consequences of potassium shifts in skeletal muscle and heart during exercise. Physiol Rev 2000; 80:1411-81. [PMID: 11015618 DOI: 10.1152/physrev.2000.80.4.1411] [Citation(s) in RCA: 350] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Since it became clear that K(+) shifts with exercise are extensive and can cause more than a doubling of the extracellular [K(+)] ([K(+)](s)) as reviewed here, it has been suggested that these shifts may cause fatigue through the effect on muscle excitability and action potentials (AP). The cause of the K(+) shifts is a transient or long-lasting mismatch between outward repolarizing K(+) currents and K(+) influx carried by the Na(+)-K(+) pump. Several factors modify the effect of raised [K(+)](s) during exercise on membrane potential (E(m)) and force production. 1) Membrane conductance to K(+) is variable and controlled by various K(+) channels. Low relative K(+) conductance will reduce the contribution of [K(+)](s) to the E(m). In addition, high Cl(-) conductance may stabilize the E(m) during brief periods of large K(+) shifts. 2) The Na(+)-K(+) pump contributes with a hyperpolarizing current. 3) Cell swelling accompanies muscle contractions especially in fast-twitch muscle, although little in the heart. This will contribute considerably to the lowering of intracellular [K(+)] ([K(+)](c)) and will attenuate the exercise-induced rise of intracellular [Na(+)] ([Na(+)](c)). 4) The rise of [Na(+)](c) is sufficient to activate the Na(+)-K(+) pump to completely compensate increased K(+) release in the heart, yet not in skeletal muscle. In skeletal muscle there is strong evidence for control of pump activity not only through hormones, but through a hitherto unidentified mechanism. 5) Ionic shifts within the skeletal muscle t tubules and in the heart in extracellular clefts may markedly affect excitation-contraction coupling. 6) Age and state of training together with nutritional state modify muscle K(+) content and the abundance of Na(+)-K(+) pumps. We conclude that despite modifying factors coming into play during muscle activity, the K(+) shifts with high-intensity exercise may contribute substantially to fatigue in skeletal muscle, whereas in the heart, except during ischemia, the K(+) balance is controlled much more effectively.
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Affiliation(s)
- O M Sejersted
- Institute for Experimental Medical Research, University of Oslo, Ullevaal Hospital, Oslo, Norway.
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