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AIM: This study explored the effects of blood flow restriction (BFR) on mRNA responses of PGC-1α (total, 1α1, and 1α4) and Na+ ,K+ -ATPase isoforms (NKA; α1-3 , β1-3 , and FXYD1) to an interval running session, and determined if these effects were related to increased oxidative stress, hypoxia, and fibre type-specific AMPK and CaMKII signalling, in human skeletal muscle.METHODS: In a randomised, crossover fashion, eight healthy men (26 ± 5 y and 57.4 ± 6.3 mL∙kg-1 ∙min-1 ) completed three exercise sessions: without (CON) or with blood flow restriction (BFR), or in systemic hypoxia (HYP, ~3250 m). A muscle sample was collected before (Pre) and after exercise (+0h, +3h) to quantify mRNA, indicators of oxidative stress (HSP27 protein in type I and II fibres, and catalase and HSP70 mRNA), metabolites, and α-AMPK Thr172 /α-AMPK, ACC Ser221 /ACC, CaMKII Thr287 /CaMKII, and PLBSer16 /PLB ratios in type I and II fibres.RESULTS: Muscle hypoxia (assessed by near-infrared spectroscopy) was matched between BFR and HYP, which was higher than CON (~90% vs. ~70%; p<0.05). The mRNA levels of FXYD1 and PGC-1α isoforms (1α1 and 1α4) increased in BFR only (p<0.05) and were associated with increases in indicators of oxidative stress and type-I fibre ACC Ser221 /ACC ratio, but dissociated from muscle hypoxia, lactate, and CaMKII signalling.CONCLUSION: Blood flow restriction augmented exercise-induced increases in muscle FXYD1 and PGC-1α mRNA in men. This effect was related to increased oxidative stress and fibre type-dependent AMPK signalling, but unrelated to the severity of muscle hypoxia, lactate accumulation, and modulation of fibre type-specific CaMKII signalling. This article is protected by copyright. All rights reserved.

Aim: This study explored the effects of blood flow restriction (BFR) on mRNA responses of PGC-1α (total, 1α1, and 1α4) and Na+,K+-ATPase isoforms (NKA; α1-3, β1-3, and FXYD1) to an interval running session and determined whether these effects were related to increased oxidative stress, hypoxia, and fibre type-specific AMPK and CaMKII signalling, in human skeletal muscle. Methods: In a randomized, crossover fashion, 8 healthy men (26 ± 5 year and 57.4 ± 6.3 mL kg−1 min−1) completed 3 exercise sessions: without (CON) or with blood flow restriction (BFR), or in systemic hypoxia (HYP, ~3250 m). A muscle sample was collected before (Pre) and after exercise (+0 hour, +3 hours) to quantify mRNA, indicators of oxidative stress (HSP27 protein in type I and II fibres, and catalase and HSP70 mRNA), metabolites, and α-AMPK Thr172/α-AMPK, ACC Ser221/ACC, CaMKII Thr287/CaMKII, and PLBSer16/PLB ratios in type I and II fibres. Results: Muscle hypoxia (assessed by near-infrared spectroscopy) was matched between BFR and HYP, which was higher than CON (~90% vs ~70%; P

Cl- channel protein 1 (ClC-1) may be important for excitability and contractility in skeletal muscle, but ClC-1 abundance has not been examined in human muscle. The aim of the present study was to examine ClC-1 abundance in human skeletal muscle, including fibre type specific differences and the effect of exercise training. A commercially available antibody was tested with positive and negative control tissue, and it recognised specifically ClC-1 in the range from 100-150 kDa. Abundance of ClC-1 was 38% higher (P < 0.01) in fast twitch Type IIa muscle fibres than in slow twitch Type I. Muscle ClC-1 abundance did not change with four weeks of training consisting of 30 min cycling at 85% of maximal heart rate (HRmax) and 3×30-s all out sprints or during a 7-week training period with 10-12×30 s uphill cycling and 4-5×~4 min cycling at 90-95% of HRmax. ClC-1 abundance correlated negatively (P < 0.01) with maximal oxygen consumption (r = -0.552) and incremental exercise performance (r = -0.546). In addition, trained cyclists had lower (P < 0.01) ClC-1 abundance than lesser trained individuals. The present observations indicate that a low abundance of muscle ClC-1 may be beneficial for exercise performance, but the role of abundance and regulation of ClC-1 in skeletal muscle of humans with respect to exercise performance and trainability need to be elucidated.

The majority of hereditary and acquired myopathies are clinically characterized by progressive muscle weakness. We hypothesized that ongoing derangement of skeletal muscle cytoarchitecture at the single fiber level may precede and be responsible for the progressive muscle weakness. Here, we analyzed the effects of aging in wild-type (wt) and heterozygous (het) and homozygous (hom) R349P desmin knock-in mice. The latter harbor the ortholog of the most frequently encountered human R350P desmin missense mutation. We quantitatively analyzed the subcellular cytoarchitecture of fast- and slow-twitch muscles from young, intermediate, and aged wt as well as desminopathy mice. We recorded multiphoton second harmonic generation and nuclear fluorescence signals in single muscle fibers to compare aging-related effects in all genotypes. The analysis of wt mice revealed that the myofibrillar cytoarchitecture remained stable with aging in fast-twitch muscles, whereas slow-twitch muscle fibers displayed structural derangements during aging. In contrast, the myofibrillar cytoarchitecture and nuclear density were severely compromised in fast- and slow-twitch muscle fibers of hom R349P desmin mice at all ages. Het mice only showed a clear degradation in their fiber structure in fast-twitch muscles from the adult to the presenescent age bin. Our study documents distinct signs of normal and R349P mutant desmin-related remodeling of the 3D myofibrillar architecture during aging, which provides a structural basis for the progressive muscle weakness. (C) 2017 Elsevier Inc. All rights reserved.

The majority of hereditary and acquired myopathies are clinically characterized by progressive muscle weakness. We hypothesized that ongoing derangement of skeletal muscle cytoarchitecture at the single fiber level may precede and be responsible for the progressive muscle weakness. Here, we analyzed the effects of aging in wild-type (wt) and heterozygous (het) and homozygous (hom) R349P desmin knock-in mice. The latter harbor the ortholog of the most frequently encountered human R350P desmin missense mutation. We quantitatively analyzed the subcellular cytoarchitecture of fast- and slow-twitch muscles from young, intermediate, and aged wt as well as desminopathy mice. We recorded multiphoton second harmonic generation and nuclear fluorescence signals in single muscle fibers to compare aging-related effects in all genotypes. The analysis of wt mice revealed that the myofibrillar cytoarchitecture remained stable with aging in fast-twitch muscles, whereas slow-twitch muscle fibers displayed structural derangements during aging. In contrast, the myofibrillar cytoarchitecture and nuclear density were severely compromised in fast- and slow-twitch muscle fibers of hom R349P desmin mice at all ages. Het mice only showed a clear degradation in their fiber structure in fast-twitch muscles from the adult to the presenescent age bin. Our study documents distinct signs of normal and R349P mutant desmin-related remodeling of the 3D myofibrillar architecture during aging, which provides a structural basis for the progressive muscle weakness. (C) 2017 Elsevier Inc. All rights reserved.

The aim of the present study was to examine fibre type-specific Na(+)-K(+) pump subunit expression and exercise-induced alterations in phospholemman (FXYD1) phosphorylation in humans. Segments of human skeletal muscle fibres were dissected and fibre typed, and protein expression was determined by Western blotting. The protein expression of the Na(+)-K(+) pump a2 isoform was lower in type I than in type II fibres (0.63 ± 0.04 a.u. vs. 1.00 ± 0.07 a.u., P <0.001), while protein expression of the Na(+)-K(+) pump a1 and ß1 isoforms was not different. Protein expression of the ATP-dependent potassium channel Kir6.2 was higher in type I compared with type II fibres. In both type I (P <0.01) and type II fibres (P <0.001) the AB_FXYD1 signal was lower after exercise compared with rest, indicating an increase in unspecific FXYD1 phosphorylation. The FXYD1 serine 68 phosphorylation was higher (P <0.001) after exercise compared with rest in type II fibres (1.90 ± 0.25 vs. 1.00 ± 0.08) and not changed in type I fibres. Total FXYD1 was not expressed in a fibre type-specific manner. Expression of phosphofructokinase was lower (P <0.001) in type I than in type II fibres, whereas citrate synthase and 3-hydroxyacyl-CoA dehydrogenase were more abundant (P <0.001) in type I fibres. In conclusion, FXYD1 phosphorylation at serine 68 increased after an acute bout of intense exercise in human type II fibres, while AB_FXYD1 signal intensity was lower in both type I and type II fibres, indicating fibre type-specific differences in FXYD1 phosphorylation on serine 63, serine 68 and threonine 69. This, together with the observation of a higher abundance of the Na(+)-K(+) pump a2 isoform protein in type II fibres, is likely to have importance for the exercise-induced human Na(+)-K(+) pump activity in the different fibre types.

The aim of the present study was to examine fibre type-specific Na(+)-K(+) pump subunit expression and exercise-induced alterations in phospholemman (FXYD1) phosphorylation in humans. Segments of human skeletal muscle fibres were dissected and fibre typed, and protein expression was determined by Western blotting. The protein expression of the Na(+)-K(+) pump a2 isoform was lower in type I than in type II fibres (0.63 ± 0.04 a.u. vs. 1.00 ± 0.07 a.u., P <0.001), while protein expression of the Na(+)-K(+) pump a1 and ß1 isoforms was not different. Protein expression of the ATP-dependent potassium channel Kir6.2 was higher in type I compared with type II fibres. In both type I (P <0.01) and type II fibres (P <0.001) the AB_FXYD1 signal was lower after exercise compared with rest, indicating an increase in unspecific FXYD1 phosphorylation. The FXYD1 serine 68 phosphorylation was higher (P <0.001) after exercise compared with rest in type II fibres (1.90 ± 0.25 vs. 1.00 ± 0.08) and not changed in type I fibres. Total FXYD1 was not expressed in a fibre type-specific manner. Expression of phosphofructokinase was lower (P <0.001) in type I than in type II fibres, whereas citrate synthase and 3-hydroxyacyl-CoA dehydrogenase were more abundant (P <0.001) in type I fibres. In conclusion, FXYD1 phosphorylation at serine 68 increased after an acute bout of intense exercise in human type II fibres, while AB_FXYD1 signal intensity was lower in both type I and type II fibres, indicating fibre type-specific differences in FXYD1 phosphorylation on serine 63, serine 68 and threonine 69. This, together with the observation of a higher abundance of the Na(+)-K(+) pump a2 isoform protein in type II fibres, is likely to have importance for the exercise-induced human Na(+)-K(+) pump activity in the different fibre types.

Christiansen, D., Bishop, D. J., Broatch, J. R., Bangsbo, J., McKenna, M. J., & Murphy, R. M. (2018). Cold-water immersion after training sessions: Effects on fiber type-specific adaptations in muscle K+ transport proteins to sprint-interval training in men. Journal of Applied Physiology, 125(2), 429-444. Available here