Role(s) of gravitational loading during developing period on the growth of rat soleus muscle fibers.
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.
Kawano
Fuminori
F
Graduate School of Medicine, Osaka University, Toyonaka City, Osaka 560-0043, Japan.
Goto
Katsumasa
K
Wang
Xiao Dong
XD
Terada
Masahiro
M
Ohira
Takashi
T
Nakai
Naoya
N
Yoshioka
Toshitada
T
Ohira
Yoshinobu
Y
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
D024461:Myosin Type I; D018995:Myosin Heavy Chains