title: Myonuclear domain and myosin phenotype in human soleus after bed rest with or without loading.
abstract: After 2 or 4 mo of bed rest (6 degrees head-down tilt) and 1 mo of ambulation, there was a tendency toward a higher percentage of fibers expressing fast myosin heavy chain (MHC) isoforms and a de novo appearance of fibers coexpressing type I+IIa+IIx and IIa+IIx MHC in human soleus fibers. After 2 and 4 mo of bed rest, the mean size of type I fibers decreased by 12 (P > 0.05) and 39%, respectively. Because myonuclear number/mm of fiber length was unchanged, myonuclear domain was smaller after bed rest than before. The mean size and myonuclear domain of type I fibers were largest after 1 mo of recovery. The effects of wearing an antigravity device (Penguin suit), which had a modest but continuous resistance at the knee and ankle (Penguin-1) or knee resistance without loading on the ankle (Penguin-2), for 10 consecutive h/day were determined during 2 mo of bed rest. Mean fiber sizes in Penguin-1, but not Penguin-2, group were maintained at or above pre-bed-rest levels, whereas neither group showed phenotype changes. Myonuclear domain in type I fibers was larger in Penguin-1 and smaller in Penguin-2 group post- compared with pre-bed rest, indicating that a single daily 10-h bout of modest muscle loading can prevent bed-rest-induced soleus fiber atrophy but has minimal effect on myosin phenotype. The specific adaptive cellular strategies involved may be a function of the duration and magnitude of the adaptive stimulus as well as the immediate activity history of the fiber before the newly changed functional demands.
authors.affiliation: Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kanoya City, Kagoshima Prefecture 891-2393, Japan. ohira@nifs-k.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Ohira
authors.forename: T
authors.initials: T
authors.lastname: Yoshinaga
authors.forename: M
authors.initials: M
authors.lastname: Ohara
authors.forename: I
authors.initials: I
authors.lastname: Nonaka
authors.forename: T
authors.initials: T
authors.lastname: Yoshioka
authors.forename: K
authors.initials: K
authors.lastname: Yamashita-Goto
authors.forename: B S
authors.initials: BS
authors.lastname: Shenkman
authors.forename: I B
authors.initials: IB
authors.lastname: Kozlovskaya
authors.forename: R R
authors.initials: RR
authors.lastname: Roy
authors.forename: V R
authors.initials: VR
authors.lastname: Edgerton
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D001835:Body Weight / Q000502:physiology; D002467:Cell Nucleus / Q000502:physiology*; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008297:Male; D018613:Microscopy, Confocal; D018485:Muscle Fibers, Skeletal / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009133:Muscular Atrophy / Q000503:physiopathology; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D009218:Myosins / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype
chemical_list: D018995:Myosin Heavy Chains; D009218:Myosins