title: Pre-power stroke cross bridges contribute to force during stretch of skeletal muscle myofibrils.
abstract: When activated skeletal muscle is stretched, force increases in two phases. This study tested the hypothesis that the increase in stretch force during the first phase is produced by pre-power stroke cross bridges. Myofibrils were activated in sarcomere lengths (SLs) between 2.2 and 2.5 microm, and stretched by approximately 5-15 per cent SL. When stretch was performed at 1 microms-1SL-1, the transition between the two phases occurred at a critical stretch (SLc) of 8.4+/-0.85 nm half-sarcomere (hs)-1 and the force (critical force; Fc) was 1.62+/-0.24 times the isometric force (n=23). At stretches performed at a similar velocity (1 microms-1SL-1), 2,3-butanedione monoxime (BDM; 1 mM) that biases cross bridges into pre-power stroke states decreased the isometric force to 21.45+/-9.22 per cent, but increased the relative Fc to 2.35+/-0.34 times the isometric force and increased the SLc to 14.6+/-0.6 nm hs-1 (n=23), suggesting that pre-power stroke cross bridges are largely responsible for stretch forces.
authors.affiliation: Department of Kinesiology and Physical Education (Faculty of Education), McGill University, 475 Pine Avenue West, Montreal, Quebec, Canada. dilson.rassier@mcgill.ca
authors.forename: Dilson E
authors.initials: DE
authors.lastname: Rassier
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000502:physiology*; D009210:Myofibrils / Q000187:drug effects / Q000502:physiology*; D012026:Reflex, Stretch / Q000187:drug effects / Q000502:physiology; D013928:Thromboxane A2
chemical_list: C004717:diacetylmonoxime; D013928:Thromboxane A2; D003931:Diacetyl