title: Electrical pulse stimulation of cultured human skeletal muscle cells as an in vitro model of exercise.
abstract: Physical exercise leads to substantial adaptive responses in skeletal muscles and plays a central role in a healthy life style. Since exercise induces major systemic responses, underlying cellular mechanisms are difficult to study in vivo. It was therefore desirable to develop an in vitro model that would resemble training in cultured human myotubes.
  
  
  
  Electrical pulse stimulation (EPS) was applied to adherent human myotubes. Cellular contents of ATP, phosphocreatine (PCr) and lactate were determined. Glucose and oleic acid metabolism were studied using radio-labeled substrates, and gene expression was analyzed using real-time RT-PCR. Mitochondrial content and function were measured by live imaging and determination of citrate synthase activity, respectively. Protein expression was assessed by electrophoresis and immunoblotting.
  
  
  
  High-frequency, acute EPS increased deoxyglucose uptake and lactate production, while cell contents of both ATP and PCr decreased. Chronic, low-frequency EPS increased oxidative capacity of cultured myotubes by increasing glucose metabolism (uptake and oxidation) and complete fatty acid oxidation. mRNA expression level of pyruvate dehydrogenase complex 4 (PDK4) was significantly increased in EPS-treated cells, while mRNA expressions of interleukin 6 (IL-6), cytochrome C and carnitin palmitoyl transferase b (CPT1b) also tended to increase. Intensity of MitoTracker®Red FM was doubled after 48 h of chronic, low-frequency EPS. Protein expression of a slow fiber type marker (MHCI) was increased in EPS-treated cells.
  
  
  
  Our results imply that in vitro EPS (acute, high-frequent as well as chronic, low-frequent) of human myotubes may be used to study effects of exercise.
authors.affiliation: Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway. natasa.nikolic@farmasi.uio.no
authors.forename: Nataša
authors.initials: N
authors.lastname: Nikolić
authors.forename: Siril Skaret
authors.initials: SS
authors.lastname: Bakke
authors.forename: Eili Tranheim
authors.initials: ET
authors.lastname: Kase
authors.forename: Ida
authors.initials: I
authors.lastname: Rudberg
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Flo Halle
authors.forename: Arild C
authors.initials: AC
authors.lastname: Rustan
authors.forename: G Hege
authors.initials: GH
authors.lastname: Thoresen
authors.forename: Vigdis
authors.initials: V
authors.lastname: Aas
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001483:Base Sequence; D002478:Cells, Cultured; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003470:Culture Media; D017931:DNA Primers; D004558:Electric Stimulation; D015444:Exercise; D005227:Fatty Acids / Q000378:metabolism; D020869:Gene Expression Profiling; D005947:Glucose / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000378:metabolism; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D019301:Oleic Acid / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D003470:Culture Media; D017931:DNA Primers; D005227:Fatty Acids; D010725:Phosphocreatine; D019301:Oleic Acid; D019344:Lactic Acid; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase; D002950:Citrate (si)-Synthase; D005947:Glucose