Joseph D Bruton

Karolinska Institutet, Solna, Stockholm, Sweden

Are you Joseph D Bruton?

Claim your profile

Publications (79)352.6 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The contractile performance of skeletal muscle declines during intense activities, i.e. fatigue develops. Fatigued muscle can enter a state of prolonged low-frequency force depression (PLFFD). PLFFD can be due to decreased tetanic free cytosolic [Ca2+] ([Ca2+]i) and/or decreased myofibrillar Ca2+ sensitivity. Increases in reactive oxygen and nitrogen species (ROS/RNS) may contribute to fatigue-induced force reductions. We studied whether pharmacological ROS/RNS inhibition delays fatigue and/or counteracts the development of PLFFD. Mechanically isolated mouse fast-twitch fibres were fatigued by sixty 150 ms, 70 Hz tetani given every 1 s. Experiments were performed in standard Tyrode solution (control) or in the presence of: NADPH oxidase (NOX) 2 inhibitor (gp91ds-tat); NOX4 inhibitor (GKT137831); mitochondria-targeted antioxidant (SS-31); nitric oxide synthase (NOS) inhibitor (L-NAME); the general antioxidant N-acetylcysteine (NAC); a cocktail of SS-31, L-NAME and NAC. Spatially- and temporally-averaged [Ca2+]i and peak force were reduced by ∼70% and ∼20% at the end of fatiguing stimulation, respectively, with no marked differences between groups. PLFFD was similar in all groups, with 30 Hz force being decreased by ∼60% at 30 min of recovery. PLFFD was mostly due to decreased tetanic [Ca2+]i in control fibres and in the presence of NOX2 or NOX4 inhibitors. Conversely, in fibres exposed to SS-31 or the anti ROS/RNS cocktail, tetanic [Ca2+]i was not decreased during recovery so PLFFD was only caused by decreased myofibrillar Ca2+ sensitivity. The cocktail also increased resting [Ca2+]i and ultimately caused cell death. In conclusion, ROS/RNS-neutralizing compounds did not counteract the force decline during or after induction of fatigue.This article is protected by copyright. All rights reserved
    The Journal of Physiology 11/2014; 593(2). DOI:10.1113/jphysiol.2014.279398 · 4.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Desmin, being a major intermediate filament of mature muscle cell, interacts with mitochondria within the cell and participates in mitochondria proper localization. The goal of the present study was to assess the effect of aggregate-prone and non-aggregate-prone desmin mutations on mitochondrial calcium uptake. Primary murine satellite cells were transduced with lentiviruses carrying desmin in wild type or mutant form, and were induced to differentiate into myotubes. Four mutations resulting in different degree of desmin aggregates formation were analyzed. Tail domain mutation Asp399Tyr has the mildest impact on desmin filament polymerization, rod domain mutation Ala357Pro causes formation of large aggregates composed of filamentous material, and Leu345Pro and Leu370Pro are considered to be the most severest in their impact on desmin polymerization and structure. For mitochondrial calcium measurement cells were loaded with rhod 2-AM. We found that aggregate-prone mutations significantly decreased [Ca(2+)]mit, whereas non-aggregate-prone mutations did not decrease [Ca(2+)]mit. Moreover aggregate-prone desmin mutations resulted in increased resting cytosolic [Ca(2+)]. However this increase was not accompanied by any alterations in sarcoplasmic reticulum calcium release. We suggest that the observed decline in [Ca(2+)]mit was due to desmin aggregate accumulation resulting in the loss of desmin mitochondria interactions.
    Cell Calcium 10/2014; DOI:10.1016/j.ceca.2014.08.001 · 4.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In cells, such as neurones and immune cells, mitochondria can form dynamic and extensive networks that change over the minute timescale. In contrast, mitochondria in adult mammalian skeletal muscle fibres show little motility over several hours. Here, we use a novel three channelled microflow device, the multifunctional pipette, to test whether mitochondria in mouse skeletal muscle connect to each other. The central channel in the pipette delivers compounds to a restricted region of the sarcolemma, typically 30 µm in diameter. Two channels on either side of the central channel use suction to create a hydrodynamically confined flow zone and remove compounds completely from the bulk solution to internal waste compartments. Compounds were delivered locally to the end or side of single adult mouse skeletal muscle fibres to test whether changes in mitochondrial membrane potential were transmitted to more distant located mitochondria. Mitochondrial membrane potential was monitored with tetramethylrhodamine ethyl ester (TMRE). Cytosolic free [Ca2+] was monitored with fluo-3. A pulse of carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP, 100 µM) applied to a small area of the muscle fibre (30 µm in diameter) produced a rapid decrease in the mitochondrial TMRE signal (indicative of depolarization) to 38% of its initial value. After washout of FCCP, the TMRE signal partially recovered. At distances greater than 50 µm away from the site of FCCP application, the mitochondrial TMRE signal was unchanged. Similar results were observed when two sites along the fibre were pulsed sequentially with FCCP. After a pulse of FCCP, cytosolic [Ca2+] was unchanged and fibres contracted in response to electrical stimulation. In conclusion, our results indicate that extensive networks of interconnected mitochondria do not exist in skeletal muscle. Furthermore, the limited and reversible effects of targeted FCCP application with the multifunctional pipette highlight its advantages over bulk application of compounds to isolated cells.
    PLoS ONE 09/2014; 9(9):e108601. DOI:10.1371/journal.pone.0108601 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Calcium (Ca2+) plays key role in muscle cell physiology, e.g. takes part in the contraction and acts as co-factor in Krebs cycle. Mitochondria are capable to uptake calcium due to close proximity to SR Ca2+ releasing microdomains. Mitochondrial calcium balance is crucial for cell destiny, increased calcium leads to apoptosis, when decreased drives autophagy. On the other hand mitochondria within the muscle cells tightly connected to desmin. In desmin knock-out mice mitochondria were non-functional. Desmin mutations are associated with developing of myopathies, however machinery remains to be elucidated. We proposed that mitochondrial failure in desmin-compromised cells might result in disturbed calcium balance. We aimed to assess impact of non-aggregate prone (D399Y) and aggregate prone (L345P, A357P, L370P) desmin mutations on mitochondrial calcium.
    Cardiovascular Research 07/2014; 103(suppl 1):S73. DOI:10.1093/cvr/cvu091.80 · 5.81 Impact Factor
  • Biophysical Journal 01/2014; 106(2):728a. DOI:10.1016/j.bpj.2013.11.4018 · 3.83 Impact Factor
  • Biophysical Journal 01/2014; 106(2):766a. DOI:10.1016/j.bpj.2013.11.4210 · 3.83 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of the general antioxidant N-acetylcysteine (NAC) on muscle function and metabolism were examined. Isolated paired mouse extensor digitorum longus muscles were studied in the absence or presence of 20 mM NAC. Muscles were electrically stimulated to perform 100 isometric tetanic contractions (300 ms duration) at frequencies resulting in ∼85 % of maximal force (70-150 Hz at 25-40 °C). NAC did not significantly affect peak force in the unfatigued state at any temperature but significantly slowed tetanic force development in a temperature-dependent fashion (e.g., time to 50 % of peak tension averaged 35 ± 2 ms [control] and 37 ± 1 ms [NAC] at 25 °C vs. 21 ± 1 ms [control] and 52 ± 6 ms [NAC, P < 0.01] at 40 °C). During repeated contractions, NAC maximally enhanced peak force by the fifth tetanus at all temperatures (by ∼30 %). Thereafter, the effect of NAC disappeared rapidly at high temperatures (35-40 °C) and more slowly at the lower temperatures (25-30 °C). At all temperatures, the enhancing effect of NAC on peak force was associated with a slowing of relaxation. NAC did not significantly affect myosin light chain phosphorylation at rest or after five contractions (∼50 % increase vs. rest). After five tetani, lactate and inorganic phosphate increased about 20-fold and 2-fold, respectively, both in control and NAC-treated muscles. Interestingly, after five tetani, the increase in glucose 6-P was ∼2-fold greater, whereas the increase in malate was inhibited by ∼75 % with NAC vs. control, illustrating the metabolic effects of NAC. NAC slightly decreased the maximum shortening velocity in early fatigue (five to seven repeated tetani). These data demonstrate that the antioxidant NAC transiently enhances muscle force generation by a mechanism that is independent of changes in myosin light chain phosphorylation and inorganic phosphate. The slowing of relaxation suggests that NAC enhances isometric force by facilitating fusion (i.e., delaying force decline between pulses). The initial slowing of tension development and subsequent slowing of relaxation suggest that NAC would result in impaired performance during a high-intensity dynamic exercise.
    Pflügers Archiv - European Journal of Physiology 08/2013; 466(3). DOI:10.1007/s00424-013-1331-z · 3.07 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Double discharges (doublets) of motor neurones at the onset of contractions increase both force and rate of force development during voluntary submaximal contractions. The purpose of this study was to examine the role of doublet discharges on force and myoplasmic free [Ca(2+)] ([Ca(2+)]i) during repeated fatiguing contractions, using a stimulation protocol mimicking the in vivo activation pattern during running. Individual intact fibres from the flexor digitorum brevis muscle of mice were stimulated at 33°C to undergo 150 constant-frequency (five pulses at 70 Hz) or doublet (an initial, extra pulse at 200 Hz) contractions at 300-ms intervals. In the unfatigued state, doublet stimulation resulted in a transient (~10-ms) approximate doubling of myoplasmic free [Ca(2+)] ([Ca(2+)]i), which was accompanied by a greater force-time integral (~70%) and peak force (~40%) compared to constant-frequency contractions. Moreover, doublets markedly increased force-time integral and peak force during the first 25 contractions of the fatiguing stimulation. In later stages of fatigue, addition of doublets increased force production but the increase in force production corresponded to only a minor portion of the fatigue-induced reduction in force. In conclusion, double discharges at the onset of contractions effectively increase force production, especially in early stages of fatigue. This beneficial effect occurs without additional force loss in later stages of fatigue, indicating that the additional energy cost induced by doublet discharges to skeletal muscle is limited.
    The Journal of Physiology 05/2013; DOI:10.1113/jphysiol.2013.257188 · 4.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVES: Polymyositis and dermatomyositis are characterised by muscle weakness and fatigue even in patients with normal muscle histology via unresolved pathogenic mechanisms. In this study, we investigated the mechanisms by which high mobility group box protein 1 (HMGB1) acts to accelerate muscle fatigue development. METHODS: Intact single fibres were dissociated from flexor digitorum brevis (FDB) of wild type, receptor for advanced glycation endproduct (RAGE) knockout and toll like receptor 4 (TLR4) knockout mice and cultured in the absence or presence of recombinant HMGB1. A decrease in sarcoplasmic reticulum Ca(2+) release during a series of 300 tetanic contractions, which reflects the development of muscle fatigue, was determined by measuring myoplasmic free tetanic Ca(2+). TLR4 and major histocompatibility complex (MHC)-class I expression in mouse FDB fibres were investigated by immunofluorescence and confocal microscopy. Immunohistochemistry was used to investigate TLR4, MHC-class I and myosin heavy chain expression in muscle fibres of patients. RESULTS: Our results demonstrate that TLR4 is expressed in human and mouse skeletal muscle fibres, and coexpressed with MHC-class I in muscle fibres of patients with myositis. Furthermore, we show that HMGB1 acts via TLR4 but not RAGE to accelerate muscle fatigue and to induce MHC-class I expression in vitro. In order to bind and signal via TLR4, HMGB1 must have a reduced cysteine 106 and a disulphide linkage between cysteine 23 and 45. CONCLUSIONS: The HMGB1-TLR4 pathway may play an important role in causing muscle fatigue in patients with polymyositis or dermatomyositis and thus is a potential novel target for future therapy.
    Annals of the rheumatic diseases 11/2012; 72(8). DOI:10.1136/annrheumdis-2012-202207 · 9.27 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mitochondrial dysfunction can drastically impair muscle function with weakness and exercise intolerance as key symptoms. Here, we examine the time course of development of muscle dysfunction in a mouse model of premature ageing induced by defective proofreading function of mitochondrial DNA (mtDNA) polymerase (mtDNA mutator mouse). Isolated fast-twitch muscles and single muscle fibres from young (3-5 months) and end-stage (11 months) mtDNAmutator mice were compared to age-matched control mice. Force and free myoplasmic [Ca2+] ([Ca2+]i) were measured under resting conditions and during fatigue induced by repeated tetani. Muscles of young mtDNA mutator mice displayed no weakness in the rested state, but had lower force and [Ca2+]I than control mice during induction of fatigue. Muscles of young mtDNA mutator showed decreased activities of citrate synthase and β-hydroxyacyl-CoA dehydrogenase, reduced expression of cytochrome c oxidase; and decreased expression of triggers of mitochondrial biogenesis (PGC-1α, PPAR α, AMPK). Muscles from end-stage mtDNA mutator mice showed weakness under resting conditions with markedly decreased tetanic [Ca2+]i, force per cross-sectional area and protein expression of the sarcoplasmic reticulum Ca2+ pump (SERCA1). In conclusion, fast-twitch muscles of prematurely ageing mtDNA mutator mice display a sequence of deleterious mitochondrial-to-nucleus signalling with an initial decrease in oxidative capacity, which was not counteracted by activation of signalling to increase mitochondrial biogenesis. This was followed by severe muscle weakness in the end-stage. These results have implication for normal ageing and suggest that decreased mitochondrial oxidative capacity due to a sedentary life style may predispose for muscle weakness developing later in life.
    The Journal of Physiology 09/2012; DOI:10.1113/jphysiol.2012.240077 · 4.54 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Dietary inorganic nitrate has profound effects on health and physiological responses to exercise. Here, we examined if nitrate, in doses readily achievable via a normal diet, could improve Ca(2+) handling and contractile function using fast- and slow-twitch skeletal muscles from C57bl/6 male mice given 1 mm sodium nitrate in water for 7 days. Age matched controls were provided water without added nitrate. In fast-twitch muscle fibres dissected from nitrate treated mice, myoplasmic free [Ca(2+)] was significantly greater than in Control fibres at stimulation frequencies from 20 to 150 Hz, which resulted in a major increase in contractile force at ≤ 50 Hz. At 100 Hz stimulation, the rate of force development was ∼35% faster in the nitrate group. These changes in nitrate treated mice were accompanied by increased expression of the Ca(2+) handling proteins calsequestrin 1 and the dihydropyridine receptor. No changes in force or calsequestrin 1 and dihydropyridine receptor expression were measured in slow-twitch muscles. In conclusion, these results show a striking effect of nitrate supplementation on intracellular Ca(2+) handling in fast-twitch muscle resulting in increased force production. A new mechanism is revealed by which nitrate can exert effects on muscle function with applications to performance and a potential therapeutic role in conditions with muscle weakness.
    The Journal of Physiology 06/2012; 590(Pt 15):3575-83. DOI:10.1113/jphysiol.2012.232777 · 4.54 Impact Factor
  • 32nd European Workshop for Rheumatology Research; 03/2012
  • Annals of the Rheumatic Diseases 02/2012; 71(Suppl 1):A42-A43. DOI:10.1136/annrheumdis-2011-201235.1 · 9.27 Impact Factor
  • Joseph D Bruton, Arthur J Cheng, Håkan Westerblad
    [Show abstract] [Hide abstract]
    ABSTRACT: Measurements of free cytosolic Ca(2+) concentration ([Ca(2+)](i)) or free Ca(2+) concentration in cellular organelles have become more routine. The primary reason for this is the availability of membrane permeant forms of Ca(2+) indicators that can easily enter cells. In this chapter, the properties required of an ideal Ca(2+) indicator are identified and the advantages and disadvantages of available Ca(2+) indicators are pointed out. The pitfalls associated with usage of Ca(2+) indicators together with the clear advantages of ratiometric over non-ratiometric indicators are discussed. The excitation of Ca(2+) indicators and detection of the emitted fluorescence light require dedicated equipment; epifluorescence or confocal microscopes are most frequently used for this purpose and the advantages and disadvantages of these are discussed. Calibration experiments are required to translate changes in the fluorescence of Ca(2+) indicators into real [Ca(2+)](i) changes, but this procedure is non-trivial and potential sources of error are identified. Future developments in the field of Ca(2+) detection are discussed.
    Advances in Experimental Medicine and Biology 01/2012; 740:27-43. DOI:10.1007/978-94-007-2888-2_2 · 2.01 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We showed previously that force development in frog and FDB mouse skeletal muscle fibres is preceded by an increase of fibre stiffness occurring well before crossbridge attachment and force generation. This stiffness increase, referred to as static stiffness, is due to a Ca(2+)-dependent stiffening of a non-crossbridge sarcomere structure which we suggested could be attributed to the titin filaments. To investigate further the role of titin in static stiffness, we measured static stiffness properties at 24 and 35°C in soleus and EDL mouse muscle fibres which are known to express different titin isoforms. We found that static stiffness was present in both soleus and EDL fibres, however, its value was about five times greater in EDL than in soleus fibres. The rate of development of static stiffness on stimulation increased with temperature and was slightly faster in EDL than in soleus in agreement with previously published data on the time course of the intracellular Ca(2+) transients in these muscles. The present results show that the presence of a non-crossbridge Ca(2+)-dependent stiffening of the muscle fibre is a physiological general characteristic of skeletal muscle. Static stiffness depends on fibre type, being greater and developing faster in fast than in slow fibres. Our observations are consistent with the idea that titin stiffening on contraction improves the sarcomere structure stability. Such an action in fact seems to be more important in EDL fast fibre than in soleus slow fibres.
    Journal of Muscle Research and Cell Motility 11/2011; 32(6):403-9. DOI:10.1007/s10974-011-9274-5 · 1.93 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fatigue occurring during exercise can be defined as the inability to maintain the initial force or power output. As fatigue becomes pronounced, force and maximum velocity of shortening are greatly reduced and force relaxation is prolonged. In principle, force loss during fatigue can result from a decrease in the number of cross-bridges generating force or a decrease of the individual cross-bridge force or to both mechanisms. The present experiments were made to investigate this point in single fibres or small fibre bundles isolated from flexor digitorum brevis (FDB) of C57BL/6 mice at 22-24◦C. During a series of 105 tetanic contractions, we measured force and fibre stiffness by applying small sinusoidal length oscillations at 2.5 or 4 kHz frequency to the activated preparation and measuring the resulting force changes. Stiffness data were corrected for the influence of compliance in series with the cross-bridge ensemble. The results show that the force decline during the first 20 tetani is due to the reduction of force developed by the individual cross-bridges and thereafter as fatigue becomes more severe, the number of cross-bridges decreases. In spite of the force reduction in the early phase of fatigue, there was an increased rate of tetanic force development and relaxation. In the latter stages of fatigue, the rate of force development and relaxation became slower. Thus, the start of fatigue is characterised by decreased cross-bridge force development and as fatigue becomes more marked, the number of cross-bridges decreases. These findings are discussed in the context of the current hypotheses about fatigue mechanisms.
    The Journal of Physiology 05/2011; 589(Pt 13):3371-81. DOI:10.1113/jphysiol.2011.209874 · 4.54 Impact Factor
  • Biophysical Journal 02/2011; 100(3). DOI:10.1016/j.bpj.2010.12.899 · 3.83 Impact Factor
  • Håkan Westerblad, Joseph D Bruton, Abram Katz
    [Show abstract] [Hide abstract]
    ABSTRACT: Skeletal muscles cope with a large range of activities, from being able to support the body weight during long periods of upright standing to perform explosive movements in response to an unexpected threat. This requires systems for energy metabolism that can provide energy during long periods of moderately increased energy consumption as well as being able to rapidly increasing the rate of energy production more than 100-fold in response to explosive contractions. In this short review we discuss how muscles can deal with these divergent demands. We first outline the major energy metabolism pathways in skeletal muscle. Next we describe metabolic differences between different muscle fiber types. Contractile performance declines during intense activation, i.e. fatigue develops, and we discuss likely underlying mechanisms. Finally, we discuss the ability of muscle fibers to adapt to altered demands, and mechanisms behind these adaptations. The accumulated experimental evidence forces us to conclude that most aspects of energy metabolism involve multiple and overlapping signaling pathways, which indicates that the control of energy metabolism is too important to depend on one single molecule or mechanism.
    Experimental Cell Research 11/2010; 316(18):3093-9. DOI:10.1016/j.yexcr.2010.05.019 · 3.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mammals exposed to a cold environment initially generate heat by repetitive muscle activity (shivering). Shivering is successively replaced by the recruitment of uncoupling protein-1 (UCP1)-dependent heat production in brown adipose tissue. Interestingly, adaptations observed in skeletal muscles of cold-exposed animals are similar to those observed with endurance training. We hypothesized that increased myoplasmic free [Ca2+] ([Ca2+]i) is important for these adaptations. To test this hypothesis, experiments were performed on flexor digitorum brevis (FDB) muscles, which do not participate in the shivering response, of adult wild-type (WT) and UCP1-ablated (UCP1-KO) mice kept either at room temperature (24°C) or cold-acclimated (4°C) for 4-5 weeks. [Ca2+]i (measured with indo-1) and force were measured under control conditions and during fatigue induced by repeated tetanic stimulation in intact single fibres. The results show no differences between fibres from WT and UCP1-KO mice. However, muscle fibres from cold-acclimated mice showed significant increases in basal [Ca2+]i (∼50%), tetanic [Ca2+]i (∼40%), and sarcoplasmic reticulum (SR) Ca2+ leak (∼fourfold) as compared to fibres from room-temperature mice. Muscles of cold-acclimated mice showed increased expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and increased citrate synthase activity (reflecting increased mitochondrial content). Fibres of cold-acclimated mice were more fatigue resistant with higher tetanic [Ca2+]i and less force loss during fatiguing stimulation. In conclusion, cold exposure induces changes in FDB muscles similar to those observed with endurance training and we propose that increased [Ca2+]i is a key factor underlying these adaptations.
    The Journal of Physiology 11/2010; 588(Pt 21):4275-88. DOI:10.1113/jphysiol.2010.198598 · 4.54 Impact Factor
  • Source
    Joseph Bruton
    The Journal of Physiology 11/2010; 588(Pt 22):4333. DOI:10.1113/jphysiol.2010.200097 · 4.54 Impact Factor

Publication Stats

2k Citations
352.60 Total Impact Points


  • 1995–2014
    • Karolinska Institutet
      • Department of Physiology and Pharmacology
      Solna, Stockholm, Sweden
  • 2009
    • Universität Ulm
      • Institute of Applied Physiology
      Ulm, Baden-Württemberg, Germany
  • 2006
    • University of Oulu
      Uleoborg, Northern Ostrobothnia, Finland
    • Oslo University Hospital
      • Institute for Experimental Medical Research
      Oslo, Oslo, Norway
  • 2002
    • VU University Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 2001
    • University of Oslo
      • Research Institute for Internal Medicine (IIM)
      Kristiania (historical), Oslo, Norway
  • 1994–1996
    • The Chinese University of Hong Kong
      • Department of Physiology
      Hong Kong, Hong Kong