title: Phenotypical transitions and Ca2+ activation properties in human muscle fibers: effects of a 60-day bed rest and countermeasures.
abstract: Muscle biopsies were taken from soleus and vastus lateralis before and after a 60-day bed rest (BR) to examine expression changes in the regulatory proteins of the thin filament and in contractile function. Twenty-four women separated in three groups were submitted to BR or a combined protocol of resistance and aerobic exercises during BR or received a supplementation of amino acids during BR. Ca(2+)-tension relationships were established in single skinned fibers identified by their myosin heavy chain and troponin C isoform expressions. Expression patterns of regulatory proteins were analyzed on muscle pieces. For both muscles, BR produced similar decreases in slow and fast fiber diameters but larger decreases in P(0) maximal forces in slow than in fast fibers. Specific forces were decreased in slow soleus and vastus fibers, which displayed a reduction in Ca(2+) affinity. These changes were accompanied by slow-to-fast transitions in regulatory proteins, with troponins C and T appearing as sensitive markers of unloading. Exercises prevented the changes in fiber diameters and forces and counteracted most of the slow-to-fast transitions. The nutrition program had a morphological beneficial effect on slow fibers. However, these fibers still presented decreases in specific P(0) after BR. Phenotypical transitions due to BR were not prevented by amino acids. Finally, in vastus lateralis muscle, BR induced a decrease in O-glycosylation level that was prevented by exercise and attenuated by nutrition. In conclusion, this study has addressed for the first time in women the respective efficiencies of two countermeasures associated with BR on muscle properties and regulatory protein expression.
authors.affiliation: Laboratoire de Plasticité Neuromusculaire, Université des Sciences et technologies de Lille, Villeneuve d'Ascq, France.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Mounier
authors.forename: Vincent
authors.initials: V
authors.lastname: Tiffreau
authors.forename: Valérie
authors.initials: V
authors.lastname: Montel
authors.forename: Bruno
authors.initials: B
authors.lastname: Bastide
authors.forename: Laurence
authors.initials: L
authors.lastname: Stevens
mesh_terms: D000199:Actins / Q000096:biosynthesis; D000328:Adult; D000597:Amino Acids, Branched-Chain / Q000494:pharmacology; D000601:Amino Acids, Essential / Q000494:pharmacology; D000693:Anaerobiosis / Q000502:physiology; D001510:Bed Rest / Q000009:adverse effects*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism; D018529:Nutritional Support; D010641:Phenotype; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation
chemical_list: D000199:Actins; D000597:Amino Acids, Branched-Chain; D000601:Amino Acids, Essential; D009124:Muscle Proteins; D018995:Myosin Heavy Chains; D002118:Calcium