title: Rigor force responses of permeabilized fibres from fast and slow skeletal muscles of aged rats.
abstract: 1. Ageing is generally associated with a decline in skeletal muscle mass and strength and a slowing of muscle contraction, factors that impact upon the quality of life for the elderly. The mechanisms underlying this age-related muscle weakness have not been fully resolved. The purpose of the present study was to determine whether the decrease in muscle force as a consequence of age could be attributed partly to a decrease in the number of cross-bridges participating during contraction. 2. Given that the rigor force is proportional to the approximate total number of interacting sites between the actin and myosin filaments, we tested the null hypothesis that the rigor force of permeabilized muscle fibres from young and old rats would not be different. 3. Permeabilized fibres from the extensor digitorum longus (fast-twitch; EDL) and soleus (predominantly slow-twitch) muscles of young (6 months of age) and old (27 months of age) male F344 rats were activated in Ca2+-buffered solutions to determine force-pCa characteristics (where pCa = -log(10)[Ca2+]) and then in solutions lacking ATP and Ca2+ to determine rigor force levels. 4. The rigor forces for EDL and soleus muscle fibres were not different between young and old rats, indicating that the approximate total number of cross-bridges that can be formed between filaments did not decline with age. We conclude that the age-related decrease in force output is more likely attributed to a decrease in the force per cross-bridge and/or decreases in the efficiency of excitation-contraction coupling.
authors.affiliation: Department of Physiology, The University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: D R
authors.initials: DR
authors.lastname: Plant
authors.forename: G S
authors.initials: GS
authors.lastname: Lynch
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002463:Cell Membrane Permeability; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D013324:Strontium / Q000494:pharmacology
chemical_list: D002118:Calcium; D013324:Strontium