Electrical Pulse Stimulation of Cultured Human Skeletal Muscle Cells as an In Vitro Model of Exercise

Background and Aims 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. Methods 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. Results 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. Conclusions 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.This work was funded by the University of Oslo, Oslo University College, the Norwegian Diabetes Foundation, the Freia Chocolade Fabriks Medical Foundation and the Anders Jahre’s Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Oxidation of methane in seawater - Laboratory experiments and the use of models - OC2022 A-114

Oxidation of methane was determined in this project by two methods: Stable isotope analyses (13CH4) and by the use of tritium-labelled methane (3H-CH4). The intentions of the project were to obtain methane oxidation rates for the marine water column, which may be of relevance for the Norwegian Continental Shelf. Experimental, sampling, and analytical methods were established for both methods. Relatively few experiments were of a quality considered to be acceptable. The oxidation data determined by the two methods resulted in half-lives of 21.6 ± 6.2 days at 5°C incubation temperature with the stable isotope method, and 5.6 ± 0.7 and 4.6 ± 2.5 days with the tritium method at 5 to 8.5°C incubation temperature, respectively. Based on the comparison to data for field studies, it seemed that the data obtained by the tritium methods represented an overestimation of methane oxidation rates, while the stable isotope data were more in agreement with field data. The oxidation data were used in model simulations to determine atmospheric releases of methane from seeps at different seep depths.Oxidation of methane in seawater - Laboratory experiments and the use of models - OC2022 A-114publishedVersio