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  • 1.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    Moberg, Marcus
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Apro, William
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    mTORC1 Signaling in Individual Human Muscle Fibers Following Resistance Exercise in Combination With Intake of Essential Amino Acids2019In: Frontiers in nutrition, ISSN 2296-861X, Vol. 6, article id 96Article in journal (Refereed)
    Abstract [en]

    Human muscles contain a mixture of type I and type II fibers with different contractile and metabolic properties. Little is presently known about the effect of anabolic stimuli, in particular nutrition, on the molecular responses of these different fiber types. Here, we examine the effect of resistance exercise in combination with intake of essential amino acids (EAA) on mTORC1 signaling in individual type I and type II human muscle fibers. Five strength-trained men performed two sessions of heavy leg press exercise. During exercise and recovery, the subjects ingested an aqueous solution of EAA (290 mg/kg) or flavored water (placebo). Muscle biopsies were taken from the vastus lateralis before and 90 min after exercise. The biopsies were freeze-dried and single fibers dissected out and weighed (range 0.95-8.1 mu g). The fibers were homogenized individually and identified as type I or II by incubation with antibodies against the different isoforms of myosin. They were also analyzed for both the levels of protein as well as phosphorylation of proteins in the mTORC1 pathway using Western blotting. The levels of the S6K1 and eEF2 proteins were similar to 50% higher in type II than in type I fibers (P < 0.05), but no difference was found between fiber types with respect to the level of mTOR protein. Resistance exercise led to non-significant increases (2-3-fold) in mTOR and S6K1 phosphorylation as well as a 50% decrease (P < 0.05) in eEF2 phosphorylation in both fiber types. Intake of EAA caused a 2 and 6-fold higher (P < 0.05) elevation of mTOR and S6K1 phosphorylation, respectively, in both type I and type II fibers compared to placebo, with no effect on phosphorylation of eEF2. In conclusion, protein levels of S6K1 and eEF2 were significantly higher in type II than type I fibers suggesting higher capacity of the mTOR pathway in type II fibers. Ingestion of EAA enhanced the effect of resistance exercise on phosphorylation of mTOR and S6K1 in both fiber types, but with considerable variation between single fibers of both types.

  • 2.
    Edman, Sebastian
    et al.
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology.
    Söderlund, Karin
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Björn Ekblom's research group.
    Blomstrand, Eva
    Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Åstrand Laboratory of Work Physiology, Eva Blomstrand's research group.
    Anabolic signalling in individual muscle fibres following resistance exercise in combination with amino acid intake: PO-2602018In: Exercise Biochemistry Review: Vol 1 No 5 (2018): Proceedings of IBEC 2018, Beijing, China (PO-201 -> PO-308), 2018Conference paper (Other academic)
    Abstract [en]

    Objective Human muscle consists of a mixture of fibres with different contractile and metabolic properties, type I (slow-twitch) and type II (fast-twitch) fibres. Little is known about the effect of anabolic stimuli, in particular nutrition, on the molecular response in the different fibre types. Here, we examine the effect of resistance exercise and essential amino acid (EAA) supplementation on mTOR signalling in individual type I and type II human muscle fibres.

    Methods Five strength-trained male subjects performed two sessions of leg press exercise (10 x 10 repetition at 62-85 % of 1RM). During exercise and recovery, the subjects ingested an aqueous solution with EAA (290 mg/kg) or flavoured water (placebo). Muscle biopsies were taken from the vastus lateralis before and 90 min after exercise. The biopsies were freeze-dried and single fibres dissected out and weighed (range 0.9 – 8 ug). The fibres were individually homogenized and analysed for proteins in the mTOR pathway using Western blot. Membranes were repeatedly stripped and fibres were identified as type I or type II following incubation with antibodies against the different myosin isoforms.

    Results Exercise led to a significant increase in mTOR and p70S6k1 phosphorylation and a fall in eEF2 phosphorylation, similar in both fibre types. There was a large variation between individual fibres; some fibres were highly activated whereas others were not activated at all despite the heavy exercise performed. Intake of EAA caused a 2- to 6-fold higher increase in mTOR and p70S6k1 phosphorylation in both type I and type II fibres as compared to intake of placebo, with no difference between the fibre types. The phosphorylation of eEF2 was not affected by intake of EAA. The total expression of p70S6k1 and eEF2 was 145% and 155% higher in type II than in type I fibres (P<0.05), respectively, whereas no difference between the fibre types was observed for mTOR protein.

    Conclusions The response to heavy resistance exercise regarding mTOR signalling was similar in type I and type II fibres in trained subjects, but with a large variation between single fibres of both types. Furthermore, ingestion of EAA enhanced the effect of resistance exercise on phosphorylation of mTOR and p70S6k1 in both fibre types.

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