Decreased hydrogen peroxide production and mitochondrial respiration in skeletal muscle but not cardiac muscle of the green-striped burrowing frog, a natural model of muscle disuse

Abstract

Suppression of disuse-induced muscle atrophy has been associated with altered mitochondrial reactive oxygen species (ROS) production in mammals. However, despite extended hindlimb immobility, aestivating animals exhibit little skeletal muscle atrophy compared with artificially immobilised mammalian models. Therefore, we studied mitochondrial respiration and ROS (H 2 O 2 ) production in permeabilised muscle fibres of the green-striped burrowing frog, Cyclorana alboguttata. Mitochondrial respiration within saponinpermeabilised skeletal and cardiac muscle fibres was measured concurrently with ROS production using high-resolution respirometry coupled to custom-made fluorometers. After 4 months of aestivation, C. alboguttata had significantly depressed whole-body metabolism bỹ 70% relative to control (active) frogs, and mitochondrial respiration in saponin-permeabilised skeletal muscle fibres decreased by almost 50% both in the absence of ADP and during oxidative phosphorylation. Mitochondrial ROS production showed up to an 88% depression in aestivating skeletal muscle when malate, succinate and pyruvate were present at concentrations likely to reflect those in vivo. The percentage ROS released per O 2 molecule consumed was also ~94% less at these concentrations, indicating an intrinsic difference in ROS production capacities during aestivation. We also examined mitochondrial respiration and ROS production in permeabilised cardiac muscle fibres and found that aestivating frogs maintained respiratory flux and ROS production at control levels. These results show that aestivating C. alboguttata has the capacity to independently regulate mitochondrial function in skeletal and cardiac muscles. Furthermore, this work indicates that ROS production can be suppressed in the disused skeletal muscle of aestivating frogs, which may in turn protect against potential oxidative damage and preserve skeletal muscle structure during aestivation and following arousal.

Mitochondrial physiology and reactive oxygen species production are altered by hypoxia acclimation in killifish (Fundulus heteroclitus)

“…Hypoxia acclimation of killifish reduced the rate of ROS release from liver mitochondria, akin to the effects of estivation on skeletal muscle mitochondria in burrowing frogs (Reilly et al, 2014), and we observed qualitatively similar effects of acclimation to constant hypoxia and intermittent hypoxia (Fig. 4).…”

Metabolic Flexibility: Hibernation, Torpor, and Estivation

“…This decrease in proton leak is greater than that seen in overwintering common frogs (see Overwintering Ectotherms, earlier) whereas mammalian heterotherms typically show no decrease in proton leak during torpor (see Turning Down ATP Supply, earlier). The suppression of mitochondrial metabolism is not seen in all tissues, including cardiac muscle of the green-striped burrowing frog (238). This result should be viewed with caution, however, as it was obtained using saponin-permeabilized tissue sections (238).…”

“…The suppression of mitochondrial metabolism is not seen in all tissues, including cardiac muscle of the green-striped burrowing frog (238). This result should be viewed with caution, however, as it was obtained using saponin-permeabilized tissue sections (238). We found recently that the inhibition of state 3 respiration of liver mitochondria isolated from hibernating thirteen lined ground squirrels is eliminated when respiration is measured from saponin-permeabilized liver slices from the same animals, implying that the procedure might reverse mechanisms underlying metabolic suppression (K. Mathers and J.…”

Mechanisms underlying inhibition of muscle disuse atrophy during aestivation in the green-striped burrowing frog, Cyclorana alboguttata

“…The suppression of ROS production and the lack of oxidative damage previously observed in the disused skeletal muscle of aestivating frogs is consistent with this hypothesis (Reilly et al, 2014;Young et al, 2013).…”

“…Given that C. albogutatta demonstrate appreciably little muscle wasting during extended periods of aestivation, the mechanisms of proteolytic control in skeletal muscle remain an interesting and unexplored avenue. In a recent study ROS production was found be suppressed in the disused skeletal muscle of aestivating frogs, which was suggested to possibly protect against potential oxidative damage and preserve skeletal muscle mass during aestivation (Reilly et al, 2014) (Chapter 3).…”