title: Role(s) of gravitational loading during developing period on the growth of rat soleus muscle fibers.
abstract: Effects of gravitational loading or unloading on the gain of the characteristics in soleus muscle fibers were studied in rats. The tail suspension was performed in newborn rats from postnatal day 4 to month 3, and the reloading was allowed for 3 mo in some rats. Single expression of type I myosin heavy chain (MHC) was observed in approximately 82% of fibers in 3-mo-old controls, but the fibers expressing multiple MHC isoforms were noted in the unloaded rats. Although 97% of fibers in 3-mo-old controls had a single neuromuscular junction at the central region of fiber, fibers with multiple nerve endplates were seen in the unloaded group. Faster contraction speed and lower maximal tension development, even after normalization with fiber size, were observed in the unloaded pure type I MHC fibers. These parameters generally returned to the age-matched control levels after reloading. It was suggested that antigravity-related tonic activity plays an important role in the gain of single neural innervation and of slow contractile properties and phenotype in soleus muscle fibers.
authors.affiliation: Graduate School of Medicine, Osaka University, Toyonaka City, Osaka 560-0043, Japan.
authors.forename: Fuminori
authors.initials: F
authors.lastname: Kawano
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Goto
authors.forename: Xiao Dong
authors.initials: XD
authors.lastname: Wang
authors.forename: Masahiro
authors.initials: M
authors.lastname: Terada
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohira
authors.forename: Naoya
authors.initials: N
authors.lastname: Nakai
authors.forename: Toshitada
authors.initials: T
authors.lastname: Yoshioka
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Ohira
mesh_terms: D000367:Age Factors; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D001835:Body Weight; D005260:Female; D006112:Gravitation; D019417:Hindlimb Suspension; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000254:growth & development* / Q000294:innervation / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D024461:Myosin Type I / Q000378:metabolism; D009469:Neuromuscular Junction / Q000502:physiology; D010641:Phenotype; D051381:Rats; D017208:Rats, Wistar; D016474:Weight-Bearing; D018474:Weightlessness Simulation
chemical_list: D024461:Myosin Type I; D018995:Myosin Heavy Chains