title: Low Po₂ conditions induce reactive oxygen species formation during contractions in single skeletal muscle fibers.
abstract: Contractions in whole skeletal muscle during hypoxia are known to generate reactive oxygen species (ROS); however, identification of real-time ROS formation within isolated single skeletal muscle fibers has been challenging. Consequently, there is no convincing evidence showing increased ROS production in intact contracting fibers under low Po₂ conditions. Therefore, we hypothesized that intracellular ROS generation in single contracting skeletal myofibers increases during low Po₂ compared with a value approximating normal resting Po₂. Dihydrofluorescein was loaded into single frog (Xenopus) fibers, and fluorescence was used to monitor ROS using confocal microscopy. Myofibers were exposed to two maximal tetanic contractile periods (1 contraction/3 s for 2 min, separated by a 60-min rest period), each consisting of one of the following treatments: high Po₂ (30 Torr), low Po₂ (3-5 Torr), high Po₂ with ebselen (antioxidant), or low Po₂ with ebselen. Ebselen (10 μM) was administered before the designated contractile period. ROS formation during low Po₂ treatment was greater than during high Po₂ treatment, and ebselen decreased ROS generation in both low- and high-Po₂ conditions (P < 0.05). ROS accumulated at a faster rate in low vs. high Po₂. Force was reduced >30% for each condition except low Po₂ with ebselen, which only decreased ~15%. We concluded that single myofibers under low Po₂ conditions develop accelerated and more oxidative stress than at Po₂ = 30 Torr (normal human resting Po₂). Ebselen decreases ROS formation in both low and high Po₂, but only mitigates skeletal muscle fatigue during reduced Po₂ conditions.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, CA, USA. zuo.4@osu.edu
authors.forename: Li
authors.initials: L
authors.lastname: Zuo
authors.forename: Amy
authors.initials: A
authors.lastname: Shiah
authors.forename: William J
authors.initials: WJ
authors.lastname: Roberts
authors.forename: Michael T
authors.initials: MT
authors.lastname: Chien
authors.forename: Peter D
authors.initials: PD
authors.lastname: Wagner
authors.forename: Michael C
authors.initials: MC
authors.lastname: Hogan
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001393:Azoles / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D000860:Hypoxia / Q000378:metabolism*; D066298:In Vitro Techniques; D054833:Isoindoles; D018613:Microscopy, Confocal; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000502:physiology; D016566:Organoselenium Compounds / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D000975:Antioxidants; D001393:Azoles; D054833:Isoindoles; D016566:Organoselenium Compounds; D017382:Reactive Oxygen Species; C042986:ebselen
keywords: confocal; ebselen; hypoxia; myofiber; reactive oxygen species