title: Passive tension of rat skeletal soleus muscle fibers: effects of unloading conditions.
abstract: In this work we studied changes in passive elastic properties of rat soleus muscle fibers subjected to 14 days of hindlimb unloading (HU). For this purpose, we investigated the titin isoform expression in soleus muscles, passive tension-fiber strain relationships of single fibers, and the effects of the thick filament depolymerization on passive tension development. The myosin heavy chain composition was also measured for all fibers studied. Despite a slow-to-fast transformation of the soleus muscles on the basis of their myosin heavy chain content, no modification in the titin isoform expression was detected after 14 days of HU. However, the passive tension-fiber strain relationships revealed that passive tension of both slow and fast HU soleus fibers increased less steeply with sarcomere length than that of control fibers. Gel analysis suggested that this result could be explained by a decrease in the amount of titin in soleus muscle after HU. Furthermore, the thick filament depolymerization was found to similarly decrease passive tension in control and HU soleus fibers. Taken together, these results suggested that HU did not change titin isoform expression in the soleus muscle, but rather modified muscle stiffness by decreasing the amount of titin.
authors.affiliation: Laboratoire de Plasticité Neuromusculaire, Université des Sciences et Technologies de Lille I, Bat SN4, F-59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Toursel
authors.forename: Laurence
authors.initials: L
authors.lastname: Stevens
authors.forename: Henk
authors.initials: H
authors.lastname: Granzier
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Mounier
mesh_terms: D000818:Animals; D064211:Connectin; D004548:Elasticity; D019417:Hindlimb Suspension / Q000502:physiology*; D007536:Isomerism; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D009124:Muscle Proteins / Q000737:chemistry / Q000378:metabolism; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D011108:Polymers / Q000378:metabolism; D011494:Protein Kinases / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000502:physiology
chemical_list: D064211:Connectin; D009124:Muscle Proteins; D011108:Polymers; D011494:Protein Kinases; D018995:Myosin Heavy Chains