title: Myosin light-chain phosphorylation and potentiation of dynamic function in mouse fast muscle.
abstract: The intent of this study was to determine if the stimulation-induced increase or "potentiation" of dynamic function of mouse extensor digitorum longus muscle (in vitro 25°C) during work cycles is graded to myosin regulatory light-chain (RLC) phosphorylation. To do this, concentric force and muscle work output during sinusoidal length changes were determined before (unpotentiated) and after (potentiated) the application of conditioning stimuli (CS) producing incremental elevations in RLC phosphorylation from rest. Sine wave excursion was from 1.09 to 0.91 of L (o) with a period of 142 ms; stimulating muscles to twitch and generate force during these cycles produced plots of force × displacement termed work loops. Stimulation at 2.5-, 5.0-, and 100-Hz elevated RLC phosphorylation from 0.16±0.02 (rest) to 0.29±0.03, 0.45±0.02 and 0.56±0.02 mol phos per mole RLC, respectively (n= 6-7, P<0.05). These CS potentiated mean concentric force (at all lengths) to 1.14±0.02, 1.26±0.04 and 1.41±0.06 of pre-stimulus, control levels (all n= 5-7, P<0.05) while work was increased to 1.07±0.02, 1.17±0.02 and 1.34±0.03 of controls, respectively. In a No CS condition that did not elevate RLC phosphorylation, neither mean concentric force nor work was altered. Thus, strong correlations between RLC phosphorylation and mean concentric force and work support the hypothesis that this molecular mechanism modulates muscle power output. No length-dependence for concentric force potentiation was observed in any condition, an outcome suggesting that interactions between instantaneous variations in muscle length and shortening velocity during work cycles modulates the potentiation response.
authors.affiliation: Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: Xeni
authors.forename: William B
authors.initials: WB
authors.lastname: Gittings
authors.forename: Daniel
authors.initials: D
authors.lastname: Caterini
authors.forename: Jiang
authors.initials: J
authors.lastname: Huang
authors.forename: Michael E
authors.initials: ME
authors.lastname: Houston
authors.forename: Robert W
authors.initials: RW
authors.lastname: Grange
authors.forename: Rene
authors.initials: R
authors.lastname: Vandenboom
mesh_terms: D000818:Animals; D005260:Female; D007537:Isometric Contraction / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D018994:Myosin Light Chains / Q000502:physiology*; D010766:Phosphorylation
chemical_list: D018994:Myosin Light Chains