title: Adaptive responses to creatine loading and exercise in fast-twitch rat skeletal muscle.
abstract: We investigated the effects of chronic creatine loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular Ca2+, and the metabolic profile in rat plantaris muscle to ascertain the bases for our previous observations that creatine loading results in a higher proportion of myosin heavy chain (MHC) IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: creatine-fed sedentary, creatine-fed run-trained, control-fed sedentary, and control-fed run-trained animals. Proportion and cross-sectional area increased 10% and 15% in type IIb fibers and the proportion of type IIa fibers decreased 11% in the creatine-fed run-trained compared with the control-fed run-trained group (P < 0.03). No differences were observed in fast Ca2+-ATPase isoform SERCA1 content (P > 0.49). Creatine feeding alone induced a 41% increase (P < 0.03) in slow Ca2+-ATPase (SERCA2) content, which was further elevated by 33% with running (P < 0.02). Run training alone reduced parvalbumin content by 50% (P < 0.05). By comparison, parvalbumin content was dramatically decreased by 75% (P < 0.01) by creatine feeding alone but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through creatine loading, alleviates the need for intracellular Ca2+ buffering by parvalbumin and increases the efficiency of Ca2+ uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated by run training (P < 0.003) but not by run training + creatine feeding. This indicates that creatine loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.
authors.affiliation: E-417 Van Vliet Centre, Univ. of Alberta, Edmonton, AB, Canada T6G 2H9. tputman@ualberta.ca).
authors.forename: Maria
authors.initials: M
authors.lastname: Gallo
authors.forename: Ian
authors.initials: I
authors.lastname: MacLean
authors.forename: Neil
authors.initials: N
authors.lastname: Tyreman
authors.forename: Karen J B
authors.initials: KJ
authors.lastname: Martins
authors.forename: Daniel
authors.initials: D
authors.lastname: Syrotuik
authors.forename: Tessa
authors.initials: T
authors.lastname: Gordon
authors.forename: Charles T
authors.initials: CT
authors.lastname: Putman
mesh_terms: D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000378:metabolism; D000222:Adaptation, Physiological; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003401:Creatine / Q000008:administration & dosage / Q000378:metabolism*; D004734:Energy Metabolism; D006019:Glycolysis; D007700:Kinetics; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism; D010641:Phenotype; D005082:Physical Exertion / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012420:Running; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism
chemical_list: C506945:Atp2a1 protein, rat; C506948:Atp2a2 protein, rat; D010320:Parvalbumins; D000255:Adenosine Triphosphate; D015094:3-Hydroxyacyl CoA Dehydrogenases; D002950:Citrate (si)-Synthase; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D003401:Creatine; D002118:Calcium