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- Rundqvist, Helene, et al.
(författare)
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Activation of the erythropoietin receptor in human skeletal muscle
- 2009
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Ingår i: European Journal of Endocrinology. - 0804-4643 .- 1479-683X. ; 161:3, s. 427-434
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Erythropoietin receptor (EPOR) expression in non-hematological tissues has been shown to be activated by locally produced and/or systemically delivered EPO. Improved oxygen homeostasis, a well-established consequence of EPOR activation, is very important for human skeletal muscle performance. In the present study we investigate whether human skeletal muscle fibers and satellite cells express EPOR and if it is activated by exercise. Design and methods: Ten healthy males performed 65 min of cycle exercise. Biopsies were obtained from the vastus lateralis muscle and femoral arterio-venous differences in EPO concentrations were estimated. Results: The EPOR proteinwas localized in areas corresponding to the sarcolemma and capillaries. Laser dissection identified EPOR mRNA expression in muscle fibers. Also, EPOR mRNA and protein were both detected in human skeletal muscle satellite cells. In the initial part of the exercise bout there was a release of EPO from the exercising leg to the circulation, possibly corresponding to an increased bioavailability of EPO. After exercise, EPOR mRNA and EPOR-associated JAK2 phosphorylation were increased. Conclusions: Interaction with JAK2 is required for EPOR signaling and the increase found in phosphorylation is therefore closely linked to the activation of EPOR. The receptor activation by acute exercise suggests that signaling through EPOR is involved in exercise-induced skeletal muscle adaptation, thus extending the biological role of EPO into the skeletal muscle.
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| 2. |
- Vollaard, Niels B. J., et al.
(författare)
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Systematic analysis of adaptations in aerobic capacity and submaximal energy metabolism provides a unique insight into determinants of human aerobic performance
- 2009
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 106:5, s. 1479-1486
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Tidskriftsartikel (refereegranskat)abstract
- Vollaard NB, Constantin-Teodosiu D, Fredriksson K, Rooyackers O, Jansson E, Greenhaff PL, Timmons JA, Sundberg CJ. Systematic analysis of adaptations in aerobic capacity and submaximal energy metabolism provides a unique insight into determinants of human aerobic performance. J Appl Physiol 106: 1479-1486, 2009. First published February 5, 2009; doi:10.1152/japplphysiol.91453.2008.-It has not been established which physiological processes contribute to endurance training-related changes (Delta) in aerobic performance. For example, the relationship between intramuscular metabolic responses at the intensity used during training and improved human functional capacity has not been examined in a longitudinal study. In the present study we hypothesized that improvements in aerobic capacity ((V) over dotO(2max)) and metabolic control would combine equally to explain enhanced aerobic performance. Twenty-four sedentary males (24 +/- 2 yr; 1.81 +/- 0.08 m; 76.6 +/- 11.3 kg) undertook supervised cycling training (45 min at 70% of pretraining (V) over dotO(2max)) 4 times/wk for 6 wk. Performance was determined using a 15-min cycling time trial, and muscle biopsies were taken before and after a 10-min cycle at 70% of pretraining (V) over dotO(2max) to quantify substrate metabolism. Substantial interindividual variability in training-induced adaptations was observed for most parameters, yet ""low responders"" for Delta(V) over dotO(2max) were not consistently low responders for other variables. While (V) over dotO(2max) and time trial performance were related at baseline (r(2) = 0.80, P < 0.001), the change in (V) over dotO(2max) was completely unrelated to the change in aerobic performance. The maximal parameters Delta(V) over dotE(max) and Delta Veq(max) (Delta(V) over dotE/(V) over dotO(2max)) accounted for 64% of the variance in Delta(V) over dotO(2max) (P < 0.001), whereas Delta performance was related to changes in the submaximal parameters Veq(submax) (r(2) = 0.33; P < 0.01), muscle Delta lactate (r(2) = 0.32; P < 0.01), and Delta acetyl-carnitine (r(2) = 0.29; P < 0.05). This study demonstrates that improvements in high-intensity aerobic performance in humans are not related to altered maximal oxygen transport capacity. Altered muscle metabolism may provide the link between training stimulus and improved performance, but metabolic parameters do not change in a manner that relates to aerobic capacity changes.
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