title: Effects of activation on the elastic properties of intact soleus muscles with a deletion in titin.
abstract: Titin has long been known to contribute to muscle passive tension. Recently, it was also demonstrated that titin-based stiffness increases upon Ca2+activation of wild-type mouse psoas myofibrils stretched beyond overlap of the thick and thin filaments. In addition, this increase in titin-based stiffness was impaired in single psoas myofibrils frommdmmice, characterized by a deletion in the N2A region of theTtngene. Here, we investigated the effects of activation on elastic properties of intact soleus muscles from wild-type andmdmmice to determine whether titin contributes to active muscle stiffness. Using load-clamp experiments, we compared the stress-strain relationships of elastic elements in active and passive muscles during unloading, and quantified the change in stiffness upon activation. Results from wild-type muscles show that upon activation, the elastic modulus increases, elastic elements develop force at 15% shorter lengths, and there was a 2.9-fold increase in the slope of the stress-strain relationship. These results are qualitatively and quantitatively similar to results from single wild-type psoas myofibrils. In contrast,mdmsoleus showed no effect of activation on the slope or intercept of the stress-strain relationship, which is consistent with impaired titin activation observed in singlemdmpsoas myofibrils. Therefore, it is likely that titin plays a role in the increase of active muscle stiffness during rapid unloading. These results are consistent with the idea that, in addition to the thin filaments, titin is activated upon Ca2+influx in skeletal muscle.
authors.affiliation: W. M. Keck Science Department, The Claremont Colleges, Claremont, CA 91711, USA jenna.monroy@gmail.com.
authors.forename: Jenna A
authors.identifier: 0000-0001-7635-8613
authors.initials: JA
authors.lastname: Monroy
authors.affiliation: Human Performance Laboratory, Department of Kinesiology, University of Calgary, Calgary, AB, Canada T2N 1N4.
authors.forename: Krysta L
authors.initials: KL
authors.lastname: Powers
authors.affiliation: Department of Biological Sciences, LeMoyne College, Syracuse, NY 13214, USA.
authors.forename: Cinnamon M
authors.initials: CM
authors.lastname: Pace
authors.affiliation: Department of Biology, Valdosta State University, Valdosta, GA 31698, USA.
authors.forename: Theodore
authors.initials: T
authors.lastname: Uyeno
authors.affiliation: Center for Bioengineering Innovation and Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA.
authors.forename: Kiisa C
authors.initials: KC
authors.lastname: Nishikawa
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D064211:Connectin / Q000235:genetics* / Q000378:metabolism; D055119:Elastic Modulus; D017353:Gene Deletion; D007537:Isometric Contraction; D051379:Mice; D008954:Models, Biological; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology*; D009136:Muscular Dystrophies / Q000235:genetics / Q000503:physiopathology*; D009220:Myositis / Q000235:genetics / Q000503:physiopathology*
chemical_list: D064211:Connectin
keywords: Connectin; Elastic recoil; Muscle activation; Muscular dystrophy with myositis (mdm); Titin