title: Mitochondrial superoxide flashes: metabolic biomarkers of skeletal muscle activity and disease.
abstract: Mitochondrial superoxide flashes (mSOFs) are stochastic events of quantal mitochondrial superoxide generation. Here, we used flexor digitorum brevis muscle fibers from transgenic mice with muscle-specific expression of a novel mitochondrial-targeted superoxide biosensor (mt-cpYFP) to characterize mSOF activity in skeletal muscle at rest, following intense activity, and under pathological conditions. Results demonstrate that mSOF activity in muscle depended on electron transport chain and adenine nucleotide translocase functionality, but it was independent of cyclophilin-D-mediated mitochondrial permeability transition pore activity. The diverse spatial dimensions of individual mSOF events were found to reflect a complex underlying morphology of the mitochondrial network, as examined by electron microscopy. Muscle activity regulated mSOF activity in a biphasic manner. Specifically, mSOF frequency was significantly increased following brief tetanic stimulation (18.1 ± 1.6 to 22.3 ± 2.0 flashes/1000 μm²·100 s before and after 5 tetani) and markedly decreased (to 7.7 ± 1.6 flashes/1000 μm²·100 s) following prolonged tetanic stimulation (40 tetani). A significant temperature-dependent increase in mSOF frequency (11.9 ± 0.8 and 19.8 ± 2.6 flashes/1000 μm²·100 s at 23°C and 37°C) was observed in fibers from RYR1(Y522S/WT) mice, a mouse model of malignant hyperthermia and heat-induced hypermetabolism. Together, these results demonstrate that mSOF activity is a highly sensitive biomarker of mitochondrial respiration and the cellular metabolic state of muscle during physiological activity and pathological oxidative stress
authors.affiliation: University of Rochester Medical Center, Department of Pharmacology and Physiology, Rochester, NY 14642, USA.
authors.forename: Lan
authors.initials: L
authors.lastname: Wei
authors.forename: Gheorghe
authors.initials: G
authors.lastname: Salahura
authors.forename: Simona
authors.initials: S
authors.lastname: Boncompagni
authors.forename: Karl A
authors.initials: KA
authors.lastname: Kasischke
authors.forename: Feliciano
authors.initials: F
authors.lastname: Protasi
authors.forename: Shey-Shing
authors.initials: SS
authors.lastname: Sheu
authors.forename: Robert T
authors.initials: RT
authors.lastname: Dirksen
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D045222:Electron Transport Chain Complex Proteins; D005786:Gene Expression Regulation / Q000502:physiology; D008164:Luminescent Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008931:Mitochondria, Muscle / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D015415:Biomarkers; D045222:Electron Transport Chain Complex Proteins; D008164:Luminescent Proteins; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D019837:Ryanodine Receptor Calcium Release Channel; C054562:yellow fluorescent protein, Bacteria; D013481:Superoxides; D000226:Mitochondrial ADP, ATP Translocases