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  • 1.
    Blackwood, Sarah J
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Katz, Abram
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Isoproterenol enhances force production in mouse glycolytic and oxidative muscle via separate mechanisms.2019In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013Article in journal (Refereed)
    Abstract [en]

    Fight or flight is a biologic phenomenon that involves activation of β-adrenoceptors in skeletal muscle. However, how force generation is enhanced through adrenergic activation in different muscle types is not fully understood. We studied the effects of isoproterenol (ISO, β-receptor agonist) on force generation and energy metabolism in isolated mouse soleus (SOL, oxidative) and extensor digitorum longus (EDL, glycolytic) muscles. Muscles were stimulated with isometric tetanic contractions and analyzed for metabolites and phosphorylase activity. Under conditions of maximal force production, ISO enhanced force generation markedly more in SOL (22%) than in EDL (8%). Similarly, during a prolonged tetanic contraction (30 s for SOL and 10 s for EDL), ISO-enhanced the force × time integral more in SOL (25%) than in EDL (3%). ISO induced marked activation of phosphorylase in both muscles in the basal state, which was associated with glycogenolysis (less in SOL than in EDL), and in EDL only, a significant decrease (16%) in inorganic phosphate (Pi). ATP turnover during sustained contractions (1 s EDL, 5 s SOL) was not affected by ISO in EDL, but essentially doubled in SOL. Under conditions of maximal stimulation, ISO has a minor effect on force generation in EDL that is associated with a decrease in Pi, whereas ISO has a marked effect on force generation in SOL that is associated with an increase in ATP turnover. Thus, phosphorylase functions as a phosphate trap in ISO-mediated force enhancement in EDL and as a catalyzer of ATP supply in SOL.

  • 2.
    Blomstrand, Eva
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Eva Blomstrand's research group.
    Krustrup, Peter
    Søndergaard, Hans
    Rådegran, Göran
    Calbet, José A L
    Saltin, Bengt
    Exercise training induces similar elevations in the activity of oxoglutarate dehydrogenase and peak oxygen uptake in the human quadriceps muscle.2011In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 462, no 2, p. 257-65Article in journal (Refereed)
    Abstract [en]

    During exercise involving a small muscle mass, peak oxygen uptake is thought to be limited by peripheral factors, such as the degree of oxygen extraction from the blood and/or mitochondrial oxidative capacity. Previously, the maximal activity of the Krebs cycle enzyme oxoglutarate dehydrogenase has been shown to provide a quantitative measure of maximal oxidative metabolism, but it is not known whether the increase in this activity after a period of training reflects the elevation in peak oxygen consumption. Fourteen subjects performed one-legged knee extension exercise for 5-7 weeks, while the other leg remained untrained. Thereafter, the peak oxygen uptake by the quadriceps muscle was determined for both legs, and muscle biopsies were taken for assays of maximal enzyme activities (at 25°C). The peak oxygen uptake was 26% higher in the trained than in the untrained muscle (395 vs. 315 ml min(-1) kg(-1), respectively; P<0.01). The maximal activities of the Krebs cycle enzymes in the trained and untrained muscle were as follows: citrate synthase, 22.4 vs. 18.2 μmol min(-1) g(-1) (23%, P<0.05); oxoglutarate dehydrogenase, 1.88 vs. 1.54 μmol min(-1) g(-1) (22%, P<0.05); and succinate dehydrogenase, 3.88 vs. 3.28 μmol min(-1) g(-1) (18%, P<0.05). The difference between the trained and untrained muscles with respect to peak oxygen uptake (80 ml min(-1) kg(-1)) corresponded to a flux through the Krebs cycle of 1.05 μmol min(-1) g(-1), and the corresponding difference in oxoglutarate dehydrogenase activity (at 38°C) was 0.83 μmol min(-1) g(-1). These parallel increases suggest that there is no excess mitochondrial capacity during maximal exercise with a small muscle mass.

  • 3.
    Gray, Stuart R
    et al.
    Institute of medical sciences, University of Aberdeen, Skottland.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Björn Ekblom's research group.
    Watson, Moira
    Ferguson, Richard A
    Skeletal muscle ATP turnover and single fibre ATP and PCr content during intense exercise at different muscle temperatures in humans.2011In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 462, no 6, p. 885-893Article in journal (Refereed)
    Abstract [en]

    The effect of temperature on skeletal muscle ATP turnover, pulmonary oxygen uptake and single fibre ATP and PCr content was studied during intense cycling exercise. Six healthy male subjects performed 6-min intense (Δ50%LT-VO(2peak)) cycling, at 60 rpm, under conditions of normal (N) and elevated muscle temperature (ET). Muscle biopsies obtained from the vastus lateralis at rest, 2 and 6 min were analysed for homogenate ATP, PCr, lactate and glycogen, allowing estimation of anaerobic ATP turnover. Freeze-dried single fibres from biopsies were characterised according to their myosin heavy chain composition (type I, IIA or IIAX) and analysed for ATP and PCr content. Pulmonary gas exchange was measured throughout. There was no difference in pulmonary oxygen uptake between the trials. The elevation of muscle temperature resulted in a lower (P < 0.05) PCr content, higher (P < 0.05) lactate content and greater (P < 0.05) anaerobic ATP turnover after 2 min of exercise. There was no effect of temperature on these measures at 6 min. In single fibres it was observed that in ET, there was a lower (P < 0.05) PCr content in type I fibres after 2 min with no differences between conditions after 6 min. The present study demonstrates that elevation of muscle temperature results in a greater anaerobic ATP turnover and type I fibre PCr degradation during the initial 2 min of intense exercise.

  • 4.
    Krustrup, Peter
    et al.
    Inst of exercise and sport sciences, Dept of human physiology August Krogh Institute University of Copenhagen.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Mohr, Magni
    Bangsbo, Jens
    The slow component of oxygen uptake during intense, sub-maximal exercise in man is associated with additional fibre recruitment.2004In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 447, no 6, p. 855-66Article in journal (Refereed)
    Abstract [en]

    Single muscle fibre metabolites and pulmonary oxygen uptake (VO2) were measured during moderate and intense, sub-maximal exercise to test the hypothesis that additional fibre recruitment is associated with the slow component of VO2. Seven healthy, male subjects performed 20 min moderate (MOD, approximately 50% of VO(2,max)) and intense (INT, approximately 80% VO(2,max)) cycling at 70 rpm. Glycogen content decreased significantly in type I and IIa fibres during INT, but only in type I fibres during MOD. During INT, creatine phosphate (CP) content decreased significantly both in types I and II fibres in the first 3 min (DeltaCP: 16.0+/-2.7 and 16.8+/-4.7 mmol kg(-1) d.w., respectively) and in the next 3 min (DeltaCP: 16.2+/-4.9 and 25.7+/-6.7 mmol kg(-1) d.w., respectively) with no further change from 6-20 min. CP content was below the pre-exercise level (mean-1 SD) in 11, 37, 70 and 74% of the type I fibres after 0, 3, 6 and 20 min of INT, respectively, and in 13, 45, 83 and 74% of the type II fibres. During INT, VO2 increased significantly by 6+/-1 and 4+/-1% in the periods 3-6 and 6-20 min, respectively (Delta VO(2,(6-3 min)): 0.14+/-0.02 l min(-1)), whereas VO2 was unchanged from 3 to 20 min of MOD. Exponential fitting revealed a slow component of VO2 during INT that appeared after approximately 2.6 min and amounted to 0.24 l min(-1). The present study demonstrates that additional type I and II fibres are recruited with time during intense sub-maximal exercise in temporal association with a significant slow component of VO2.

  • 5.
    Krustrup, Peter
    et al.
    Inst of exercise and sport sciences, dept of human physiology, August Krogh Institut, University of Copenhagen.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Mohr, Magni
    González-Alonso, José
    Bangsbo, Jens
    Recruitment of fibre types and quadriceps muscle portions during repeated, intense knee-extensor exercise in humans.2004In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 449, no 1, p. 56-65Article in journal (Refereed)
    Abstract [en]

    To investigate recruitment of slow-twitch (ST) and fast-twitch (FT) muscle fibres, as well as the involvement of the various quadriceps femoris muscle portions during repeated, intense, one-legged knee-extensor exercise, 12 healthy male subjects performed two 3-min exercise bouts at approximately 110% maximum thigh O2 consumption (EX1 and EX2) separated by 6 min rest. Single-fibre metabolites were determined in successive muscle biopsies obtained from the vastus lateralis muscle (n = 6) and intra-muscular temperatures were continuously measured at six quadriceps muscle sites (n = 6). Creatine phosphate (CP) had decreased (P < 0.05) by 27, 73 and 88% in ST fibres and 25, 71 and 89% in FT fibres after 15 and 180 s of EX1 and after 180 s of EX2, respectively. CP was below resting mean-1 SD in 15, 46, 84 and 100% of the ST fibres and 9, 48, 85 and 100% of the FT fibres at rest, after 15 and 180 s of EX1 and after 180 s of EX2, respectively. A significant muscle temperature increase (deltaTm) occurred within 2-4 s at all quadriceps muscle sites. DeltaTm varied less than 10% between sites during EX1, but was 23% higher (P < 0.05) in the vastus lateralis than in the rectus femoris muscle during EX2. DeltaTm in the vastus lateralis was 101 and 109% of the mean quadriceps value during EX1 and EX2, respectively. We conclude that both fibre types and all quadriceps muscle portions are recruited at the onset of intense knee-extensor exercise, that essentially all quadriceps muscle fibres are activated during repeated intense exercise and that metabolic measurements in the vastus lateralis muscle provide a good indication of the whole-quadriceps muscle metabolism during repeated, intense, one-legged knee-extensor exercise.

  • 6.
    Tonkonogi, Michail
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Fernström, Maria
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Walsh, Brandon
    Ji, Li Li
    Rooyackers, Olav
    Hammarqvist, Folke
    Wernerman, Jan
    Sahlin, Kent
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Research group for Mitokondriell funktion och metabolisk kontroll.
    Reduced oxidative power but unchanged antioxidative capacity in skeletal muscle from aged humans.2003In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 446, no 2, p. 261-9Article in journal (Refereed)
    Abstract [en]

    The hypothesis that the aging process is associated with mitochondrial dysfunction and oxidative stress has been investigated in human skeletal muscle. Muscle biopsy samples were taken from seven old male subjects [OS; 75 (range 61-86) years] and eight young male subjects [YS; 25 (22-31) years]. Oxidative function was measured both in permeabilised muscle fibres and isolated mitochondria. Despite matching the degree of physical activity, OS had a lower training status than YS as judged from pulmonary maximal O(2) consumption ( Vdot;O(2)max, -36%) and handgrip strength (-20%). Both maximal respiration and creatine-stimulated respiration were reduced in muscle fibres from OS (-32 and -34%, respectively). In contrast, respiration in isolated mitochondria was similar in OS and YS. The discrepancy might be explained by a biased harvest of "healthy" mitochondria and/or disruption of structural components during the process of isolation. Cytochrome C oxidase was reduced (-40%, P<0.01), whereas UCP3 protein tended to be elevated in OS ( P=0.09). Generation of reactive oxygen species by isolated mitochondria and measures of antioxidative defence (muscle content of glutathione, glutathione redox status, antioxidative enzymes activity) were not significantly different between OS and YS. It is concluded that aging is associated with mitochondrial dysfunction, which appears to be unrelated to reduced physical activity. The hypothesis of increased oxidative stress in aged muscle could not be confirmed in this study.

  • 7.
    Tonkonogi, Michail
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences.
    Walsh, Brandon
    Tiivel, T
    Saks, V
    Sahlin, Kent
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Research group for Mitokondriell funktion och metabolisk kontroll.
    Mitochondrial function in human skeletal muscle is not impaired by high intensity exercise.1999In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 437, no 4, p. 562-8Article in journal (Refereed)
    Abstract [en]

    The hypothesis that high-intensity (HI) intermittent exercise impairs mitochondrial function was investigated with different microtechniques in human muscle samples. Ten male students performed three bouts of cycling at 130% of peak O2 consumption (V.O2,peak). Muscle biopsies were taken from the vastus lateralis muscle at rest, at fatigue and after 110 min recovery. Mitochondrial function was measured both in isolated mitochondria and in muscle fibre bundles made permeable with saponin (skinned fibres). In isolated mitochondria there was no change in maximal respiration, rate of adenosine 5'-triphosphate (ATP) production (measured with bioluminescence) and respiratory control index after exercise or after recovery. The ATP production per consumed oxygen (P/O ratio) also remained unchanged at fatigue but decreased by 4% (P<0.05) after recovery. In skinned fibres, maximal adenosine 5'-diphosphate (ADP)-stimulated respiration increased by 23% from rest to exhaustion (P<0.05) and remained elevated after recovery, whereas the respiratory rates in the absence of ADP and at 0.1 mM ADP (submaximal respiration) were unchanged. The ratio between respiration at 0.1 and 1 mM ADP (ADP sensitivity index) decreased at fatigue (P<0.05) but after the recovery period was not significantly different from that at rest. It is concluded that mitochondrial oxidative potential is maintained or improved during exhaustive HI exercise. The finding that the sensitivity of mitochondrial respiration to ADP is reversibly decreased after strenuous exercise may indicate that the control of mitochondrial respiration is altered.

  • 8. Tsuchida, Hiroki
    et al.
    Björnholm, Marie
    Fernström, Maria
    Karolinska institutet.
    Galuska, Dana
    Johansson, Per
    Wallberg-Henriksson, Harriet
    Zierath, Juleen R
    Lake, Staffan
    Krook, Anna
    Gene expression of the p85alpha regulatory subunit of phosphatidylinositol 3-kinase in skeletal muscle from type 2 diabetic subjects.2002In: Pflügers Archiv: European Journal of Physiology, ISSN 0031-6768, E-ISSN 1432-2013, Vol. 445, no 1, p. 25-31Article in journal (Refereed)
    Abstract [en]

    The gene of the p85alpha regulatory subunit of phosphatidylinositol (PI) 3-kinase gives rise to several splice variants. We hypothesized that the expression of p85alpha splice variants may be altered in skeletal muscle from subjects with type 2 diabetes mellitus. Skeletal muscle biopsies were obtained from nine type 2 diabetic and eight healthy men, matched for age, body mass index (BMI) and physical fitness. PI 3-kinase activity in skeletal muscle following in vitro insulin stimulation was reduced in subjects with type 2 diabetes. p85alpha mRNA was elevated fourfold in type 2 diabetic as compared to healthy control subjects ( P<0.05). p85alpha mRNA abundance was positively correlated with plasma insulin concentration ( P<0.01) and serum glucose concentration ( P<0.01). Despite this, protein levels of p85alpha, p55alpha, and the novel human p50alpha were not altered in type 2 diabetic subjects. Thus, although gene expression of full-length p85alpha is increased in skeletal muscle from type 2 diabetics, this is not reflected by increased protein levels. Therefore, defects in PI 3-kinase activity are likely due to impaired activation of the enzyme rather than changes in protein expression of the isoforms of the regulatory subunit.

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