title: Creatine loading elevates the intracellular phosphorylation potential and alters adaptive responses of rat fast-twitch muscle to chronic low-frequency stimulation.
abstract: This study tested the hypothesis that elevating the intracellular phosphorylation potential (IPP = [ATP]/[ADP]free) within rat fast-twitch tibialis anterior muscles by creatine (Cr) loading would prevent fast-to-slow fibre transitions induced by chronic low-frequency electrical stimulation (CLFS, 10 Hz, 12 h/day). Creatine-control and creatine-CLFS groups drank a solution of 1% Cr + 5% dextrose, ad libitum, for 10 days before and during 10 days of CLFS; dextrose-control and dextrose-CLFS groups drank 5% dextrose. Cr loading increased total Cr (P < 0.025), phosphocreatine (PCr) (P < 0.003), and the IPP (P < 0.0008) by 34%, 45%, and 64%, respectively. PCr and IPP were 46% (P < 0.002) and 76% (P < 0.02) greater in creatine-CLFS than in dextrose-CLFS. Higher IPP was confirmed by a 58% reduction in phospho-AMP-activated protein kinase α (Thr172) (P < 0.006). In dextrose-CLFS, myosin heavy chain (MyHC) I and IIa transcripts increased 32- and 38-fold (P < 0.006), respectively, whereas MyHC-IIb mRNA decreased by 75% (P < 0.03); the corresponding MyHC-I and MyHC-IIa protein contents increased by 2.0- (P < 0.03) and 2.7-fold (P < 0.05), respectively, and MyHC-IIb decreased by 30% (P < 0.03). In contrast, within creatine-CLFS, MyHC-I and MyHC-IIa mRNA were unchanged and MyHC-IIb mRNA decreased by 75% (P < 0.003); the corresponding MyHC isoform contents were not altered. Oxidative reference enzymes were similarly elevated (P < 0.01) in dextrose-CLFS and creatine-CLFS, but reciprocal reductions in glycolytic reference enzymes occurred only in dextrose-CLFS (P < 0.02). Preservation of the glycolytic potential and greater SERCA2 and parvalbumin contents in creatine-CLFS coincided with prolonged time to peak tension and half-rise time (P < 0.01). These results highlight the IPP as an important physiological regulator of muscle fibre plasticity and demonstrate that training-induced changes typically associated with improvements in muscular endurance or increased power output are not mutually exclusive in Cr-loaded muscles.
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.|b The Centre for Neuroscience, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2E1, Canada.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Putman
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.
authors.forename: Maria
authors.initials: M
authors.lastname: Gallo
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.
authors.forename: Karen J B
authors.initials: KJ
authors.lastname: Martins
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.
authors.forename: Ian M
authors.initials: IM
authors.lastname: MacLean
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: Jendral
authors.affiliation: b The Centre for Neuroscience, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2E1, Canada.|d Division of Physical Medicine and Rehabilitation, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T5G 0B7, Canada.
authors.forename: Tessa
authors.initials: T
authors.lastname: Gordon
authors.affiliation: a Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB T6G 2H9, Canada.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Syrotuik
authors.affiliation: c Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5, Canada.
authors.forename: Walter T
authors.initials: WT
authors.lastname: Dixon
mesh_terms: D000818:Animals; D003401:Creatine / Q000494:pharmacology*; D004558:Electric Stimulation; D005947:Glucose / Q000008:administration & dosage; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects* / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000187:drug effects / Q000378:metabolism; D010725:Phosphocreatine / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects* / Q000502:physiology*; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D010725:Phosphocreatine; D011494:Protein Kinases; D018995:Myosin Heavy Chains; D005947:Glucose; D003401:Creatine
keywords: CFLS; CLFS; PAGE en présence de SDS; RT-PCR en temps réel; SDS-PAGE; SERCA1; SERCA2; chaîne lourde de myosine; contractile function; enzymes métaboliques de référence; fonction contractile; metabolic reference enzymes; myosin heavy chain; parvalbumin; parvalbumine; real-time RT-PCR