title: Effect of strain on actomyosin kinetics in isometric muscle fibers.
abstract: Investigations were conducted into the biochemical and mechanical states of cross-bridges during isometric muscle contraction. Rapid length steps (3 or 6 nm hs(-1)) were applied to rabbit psoas fibers, permeabilized and isometric, at either 12 degrees C or 20 degrees C. Fibers were activated by photolysis of P(3)-1-(2-nitrophenyl)-ethyl ester of ATP infused into rigor fibers at saturating Ca(2+). Sarcomere length, tension, and phosphate release were recorded-the latter using the MDCC-PBP fluorescent probe. A reduction in strain, induced by a rapid release step, produced a short-lived acceleration of phosphate release. Rates of the phosphate transient and that of phases 3 and 4 of tension recovery were unaffected by step size but were elevated at higher temperatures. In contrast the amplitude of the phosphate transient was smaller at 20 degrees C than 12 degrees C. The presence of 0.5 or 1.0 mM added ADP during a release step reduced both the rate of tension recovery and the poststep isometric tension. A kinetic scheme is presented to simulate the observed data and to precisely determine the rate constants for the elementary steps of the ATPase cycle.
authors.affiliation: Division of Biomedical Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: V B
authors.initials: VB
authors.lastname: Siththanandan
authors.forename: J L
authors.initials: JL
authors.lastname: Donnelly
authors.forename: M A
authors.initials: MA
authors.lastname: Ferenczi
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003198:Computer Simulation; D004548:Elasticity; D007537:Isometric Contraction / Q000502:physiology*; D007700:Kinetics; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits; D012518:Sarcomeres / Q000502:physiology*; D013314:Stress, Mechanical
chemical_list: D000199:Actins; D020409:Molecular Motor Proteins; D009218:Myosins