Low P o 2 conditions induce reactive oxygen species formation during contractions in single skeletal muscle fibers

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology integrative and comparative physiology, 2013-06, Vol.304 (11), p.R1009-R1016
• Main Authors: Zuo, Li, Shiah, Amy, Roberts, William J., Chien, Michael T., Wagner, Peter D., Hogan, Michael C.
• Format: Article
• Language: English
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00563.2012

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 Po 2 conditions. Therefore, we hypothesized that intracellular ROS generation in single contracting skeletal myofibers increases during low Po 2 compared with a value approximating normal resting Po 2 . 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 Po 2 (30 Torr), low Po 2 (3–5 Torr), high Po 2 with ebselen (antioxidant), or low Po 2 with ebselen. Ebselen (10 μM) was administered before the designated contractile period. ROS formation during low Po 2 treatment was greater than during high Po 2 treatment, and ebselen decreased ROS generation in both low- and high-Po 2 conditions ( P < 0.05). ROS accumulated at a faster rate in low vs. high Po 2 . Force was reduced >30% for each condition except low Po 2 with ebselen, which only decreased ∼15%. We concluded that single myofibers under low Po 2 conditions develop accelerated and more oxidative stress than at Po 2 = 30 Torr (normal human resting Po 2 ). Ebselen decreases ROS formation in both low and high Po 2 , but only mitigates skeletal muscle fatigue during reduced Po 2 conditions.