title: Force generation, but not myosin ATPase activity, declines with age in rat muscle fibers.
abstract: We tested the hypothesis that age-associated decline in muscle function is related to a change in myosin ATPase activity. Single, glycerinated semimembranosus fibers from young (8-12 mo) and aged (32-37 mo) Fischer 344 x Brown Norway male rats were analyzed simultaneously for force and myosin ATPase activity over a range of Ca2+ concentrations. Maximal force generation was ~20% lower in fibers from aged animals (P = 0.02), but myosin ATPase activity was not different between fibers from young and aged rats: 686 +/- 46 (n = 30) and 697 +/- 46 microM/s (n = 33) (P = 0.89). The apparent rate constant for the dissociation of strong-binding myosin from actin was calculated to be ~30% greater in fibers from aged animals (P = 0.03), indicating that the lower force produced by fibers from aged animals is due to a greater flux of myosin heads from the strong-binding state to the weak-binding state during contraction. This is in agreement with our previous electron paramagnetic resonance experiments that showed a reduced fraction of myosin heads in the strong-binding state during a maximal isometric contraction in fibers from older rats.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA. dl@ddt.biochem.umn.edu
authors.forename: Dawn A
authors.initials: DA
authors.lastname: Lowe
authors.forename: David D
authors.initials: DD
authors.lastname: Thomas
authors.forename: LaDora V
authors.initials: LV
authors.lastname: Thompson
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000375:Aging / Q000502:physiology*; D000818:Animals; D066298:In Vitro Techniques; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D011914:Rats, Inbred BN; D011916:Rats, Inbred F344
chemical_list: D020033:Protein Isoforms; D000255:Adenosine Triphosphate; D018995:Myosin Heavy Chains; D009218:Myosins