Fig. 5.

Oxygen consumption and substrate use in L6, C2C12, and human primary myotubes. A and B: mRNA expression of lactate dehydrogenase subunits (LDHA, LDHB). C: extracellular acidification rate (ECAR) during a Mito Stress Test measured with Seahorse technology. Means ± SE; n totals are as follows: HSMC: n = 13 replicates from 8 independent donors, C2C12: n = 7 independent experiments, L6: n = 8 independent experiments, two-way ANOVA with Tukey’s multiple comparison. D: lactate accumulation in the extracellular medium measured as described in methods. Box-and-whisker Tukey plot; n totals are as follows: HSMC: n = 5 replicates from 4 independent donors, C2C12: n = 5 independent experiments, L6: n = 5 independent experiments, one-way ANOVA with Tukey’s multiple comparison, *P < 0.05, **P < 0.01. E: mRNA expression of mitochondrial complexes. F: oxygen consumption rate (OCR) during a Mito Stress Test measured with Seahorse technology. Means ± SE; n totals are as follows: HSMC: n = 13 replicates from 8 independent donors, C2C12: n = 7 independent experiments, L6: n = 8 independent experiments, two-way ANOVA with Tukey’s multiple comparison, *P < 0.05 compared with both C2C12 and human skeletal muscle cells (HSMC), †P < 0.05 compared with C2C12 and L6. G: energy plot from the Mito Stress Test. H: unstimulated fatty acid oxidation, measured by the oxidation of [³H]palmitate into H₂O. Box-and-whisker Tukey plot; n totals are as follows: HSMC: n = 37 replicates from 12 independent donors, C2C12: n = 11 independent experiments, L6: n = 17 independent experiments, one-way ANOVA with Tukey’s multiple comparison. I: basal glucose oxidation as measured by the oxidation of [¹⁴C]glucose into CO₂. Box-and-whisker Tukey plot; n totals are as follows: HSMC: n = 19 replicates from 12 independent donors, C2C12: n = 6 independent experiments, L6: n = 8 independent experiments, one-way ANOVA with Tukey’s multiple comparison, *P < 0.05. J: carbonyl cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP)-stimulated [¹⁴C]glucose oxidation. Means ± SE and individual data points; n totals are as follows: HSMC: n = 19 replicates from 12 independent donors, C2C12: n = 6 independent experiments, L6: n = 7 independent experiments, one-way ANOVA with Tukey’s multiple comparison, †P < 0.05 effect of FCCP vs. unstimulated. OXPHOS, oxidative phosphorylation.