title: The cellular stress response of rat skeletal muscle following lengthening contractions.
abstract: The cellular stress response of the rat tibialis anterior (TA) muscle was investigated following 20, 40, or 60 lengthening contractions (LCs) using an in vivo model of electrical stimulation. Muscles were removed at 0, 1, 3, or 24 h after LCs and assessed for heat shock transcription factor (HSF) activation, heat shock protein (HSP) content, and/or morphological evidence of muscle fibre damage. When compared with the first muscle contraction, peak muscle torque was reduced by 26% (p < 0.05) after 20 LCs and further reduced to 56% and 60% (p < 0.001) after 40 and 60 LCs, respectively. Following 60 LCs, HSF activation was detected at 0, 1, and 3 h but was undetectable at 24 h. Hsp72 content was elevated at 24 h after 20 LCs (2.34 ± 0.37 fold, p < 0.05), 40 LCs (3.02 ± 0.31 fold, p < 0.01), and 60 LCs (3.37 ± 0.21 fold, p < 0.001). Hsp25 content increased after 40 (2.36 ± 0.24 fold, p < 0.01) and 60 LCs (2.80 ± 0.37 fold, p < 0.01). Morphological assessment of TA morphology revealed that very few fibres were damaged following 20 LCs while multiple sets of LCs (40 and 60) caused greater amounts of fibre damage. Electron microscopy showed disrupted Z-lines and sarcomeres were detectable in some muscles fibres following 20 LCs but were more prevalent and severe in muscles subjected to 40 or 60 LCs. These results suggest LCs elevate HSP content by an HSF-mediated mechanism (60 LC) and a single set of 20 LCs is capable of increasing muscle HSP content without causing significant muscle fibre damage.
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON M5S 2W6, Canada.|Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON M5S 2W6, Canada.
authors.forename: Evan
authors.initials: E
authors.lastname: Pollock-Tahiri
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON M5S 2W6, Canada.|Faculty of Kinesiology and Physical Education, University of Toronto, Toronto, ON M5S 2W6, Canada.
authors.forename: Marius
authors.initials: M
authors.lastname: Locke
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism; D050884:HSP72 Heat-Shock Proteins / Q000378:metabolism; D000076249:Heat Shock Transcription Factors / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological
chemical_list: D055551:HSP27 Heat-Shock Proteins; D050884:HSP72 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; C486114:Hspb1 protein, rat
keywords: contractions pliométriques; facteur de transcription associé au choc thermique; heat shock proteins; heat shock transcription factor; jambier antérieur; lengthening muscle contractions; lésion musculaire; muscle damage; protéines de choc thermique; tibialis anterior