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- Norman, B, et al.
(author)
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ACTN3 genotype and modulation of skeletal muscle response to exercise in human subjects
- 2014
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In: Journal of applied physiology (Bethesda, Md. : 1985). - : American Physiological Society. - 1522-1601 .- 8750-7587. ; 116:9, s. 1197-1203
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Journal article (peer-reviewed)abstract
- α-Actinin-3 is a Z-disc protein expressed only in type II muscle fibers. A polymorphism in the ACTN3 gene (R577X) results in lack of α-actinin-3 in XX genotype. The prevalence of the mutated X-allele is lower among power/sprint oriented athletes compared with controls, indicating that the lack of α-actinin-3 is detrimental in these sports, but a mechanistic link has not been established. Results from Actn3-knockout (KO) mouse model suggest that α-actinin-3 may affect muscle mass and muscle glycogen levels. In the present investigation we examined muscle fiber type composition, cross-sectional fiber area (CSA), and muscle glycogen levels at baseline in 143 human subjects with different ACTN3 genotypes. In addition, hypertrophy signaling and glycogen utilization in response to sprint exercise were studied in a subset of subjects. Glycogen utilization was analyzed in separate pools of type I and type II fibers. No differences in fiber type composition, CSA, or muscle glycogen levels were observed at baseline across the ACTN3 genotypes. However, the sprint exercise-induced increase in phosphorylation of mTOR and p70S6k was smaller in XX than in RR+RX ( P = 0.03 and P = 0.01, respectively), indicating a less pronounced activation of hypertrophy signaling in XX. Glycogen utilization during sprint exercise varied across ACTN3 genotypes in type II fibers ( P = 0.03) but not in type I fibers ( P = 0.38). The present results are in accordance with findings from the KO mice and reinforce the hypothesis that ACTN3 genotype-associated differences in muscle mass and glycogen utilization provide a mechanistic explanation for the modulation of human performance by the ACTN3 genotype.
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- Glenmark, B, et al.
(author)
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Difference in skeletal muscle function in males vs. females: role of estrogen receptor-beta
- 2004
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In: American journal of physiology. Endocrinology and metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 287:6, s. E1125-E1131
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Journal article (peer-reviewed)abstract
- Male skeletal muscles are generally faster and have higher maximum power output than female muscles. Conversely, during repeated contractions, female muscles are generally more fatigue resistant and recover faster. We studied the role of estrogen receptor-β (ERβ) in this gender difference by comparing contractile function of soleus (mainly slow-twitch) and extensor digitorum longus (fast-twitch) muscles isolated from ERβ-deficient (ERβ−/−) and wild-type mice of both sexes. Results showed generally shorter contraction and relaxation times in male compared with female muscles, and ERβ deficiency had no effect on this. Fatigue (induced by repeated tetanic contractions) and recovery of female muscles were not affected by ERβ deficiency. However, male ERβ−/− muscles were slightly more fatigue resistant and produced higher forces during the recovery period than wild-type male muscles. In fact, female muscles and male ERβ−/− muscles displayed markedly better recovery than male wild-type muscles. Gene screening of male soleus muscles showed 25 genes that were differently expressed in ERβ−/− and wild-type mice. Five of these genes were selected for further analysis: muscle ankyrin repeat protein-2, muscle LIM protein, calsequestrin, parvalbumin, and aquaporin-1. Expression of these genes showed a similar general pattern: increased expression in male and decreased expression in female ERβ−/− muscles. In conclusion, ERβ deficiency results in increased performance during fatigue and recovery of male muscles, whereas female muscles are not affected. Improved contractile performance of male ERβ−/− mouse muscles was associated with increased expression of mRNAs encoding important muscle proteins.
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