title: Profiles of connectin (titin) in atrophied soleus muscle induced by unloading of rats.
abstract: Responses of the properties of connectin molecules in the slow-twitch soleus (Sol) and fast-twitch extensor digitorum longus muscles of rats to 3 days of unloading with or without 3-day reloading were investigated. The wet weight (relative to body wt) of Sol, not of extensor digitorum longus, in the unloaded group was significantly less than in the age-matched control (P < 0.05). Immunoelectron microscopic analyses showed that a monoclonal antibody against connectin (SM1) bound to the I-band region close to the edge of the A band at resting length and moved reversibly away from the Z line as the muscle fibers were stretched. In Sol, the displacement of the SM1-bound dense spots in response to stretching decreased after hindlimb suspension. There were no changes in the molecular weights and the percent distributions of alpha- and beta-connectin in both muscles after hindlimb suspension. A significant increment of percent beta-connectin in Sol was observed after 3 days of reloading after hindlimb suspension (P < 0.05). It is suggested that the elasticity of connectin filaments in the I-band region of the atrophied Sol fibers was reduced relative to that of the control fibers. The lack of the elasticity in atrophied muscle fibers may cause a decrease in contractile function.
authors.affiliation: Department of Physiology, St. Marianna University School of Medicine, Miyamae, Kawasaki City, Kanagawa 216-8511, USA.
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Goto
authors.forename: Ryoko
authors.initials: R
authors.lastname: Okuyama
authors.forename: Masanori
authors.initials: M
authors.lastname: Honda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Uchida
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Akema
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Ohira
authors.forename: Toshitada
authors.initials: T
authors.lastname: Yoshioka
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal; D064211:Connectin; D004548:Elasticity; D004591:Electrophoresis, Polyacrylamide Gel; D019417:Hindlimb Suspension / Q000502:physiology*; D008297:Male; D016253:Microscopy, Immunoelectron; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology*; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000911:Antibodies, Monoclonal; D064211:Connectin; D009124:Muscle Proteins; D011494:Protein Kinases