Effect of conditioning and physiological hyperthermia on canine skeletal muscle mitochondrial oxygen consumption

Abstract

Exercise often causes skeletal muscle hyperthermia, likely resulting in decreased efficiency of mitochondrial respiration. We hypothesized that athletic conditioning would improve mitochondrial tolerance to hyperthermia. Skeletal muscle biopsies were obtained from 6 Alaskan sled dogs under light general anesthesia before and after a full season of conditioning and racing, and respiration of permeabilized muscle fibers was measured at 38, 40, 42, and 44°C. There was no effect of temperature on phosphorylating respiration, and athletic conditioning increased maximal phosphorylating respiration by 19%. Leak respiration increased and calculated efficiency of oxidative phosphorylation decreased with increasing incubation temperature, and athletic conditioning resulted in higher leak respiration and lower calculated oxidative phosphorylation efficiency at all temperatures. Conditioning increased skeletal muscle expression of putative mitochondrial leak pathways adenine nucleotide transporter 1 and uncoupling protein 3, both of which were correlated with the magnitude of leak respiration. We conclude that athletic conditioning in elite canine endurance athletes results in increased capacity for mitochondrial proton leak that potentially reduces maximal mitochondrial membrane potential during periods of high oxidative phosphorylation. This effect may provide a mechanistic explanation for previously-reported decreases in exercise-induced muscle damage in well-conditioned subjects.

Conditioning-induced expression of novel glucose transporters in canine skeletal muscle homogenate

“…The results of this study may help explain the metabolic strategies that produce the impressive exercise capacity of highly conditioned athletic dogs. The typical conditioning program for ultraendurance sled dog racing has been shown to increase muscle oxidative capacity [ 27 , 28 ] without evidence of fiber type switching (based on myosin ATPase staining) [ 29 ]. Despite a diet that is strikingly high in fat [ 29 , 30 ], conditioning for endurance exercise in these athletes results in a distinct glucocentric metabolic strategy [ 31 ] characterized by high stimulus for hepatic glucose output during exercise [ 32 ] and increased capacity for peripheral glucose clearance [ 9 ].…”

A practical perspective on how to develop, implement, execute, and reproduce high‐resolution respirometry experiments: The physiologist's guide to an Oroboros O2k

“…39 However, upon addition of rotenone the differences were eliminated suggesting that the effects of exercise primarily improve complex I function in this impressive model of mitochondrial function. 39 Designing an O2k protocol should also include consideration for other aspects of the cell environment that can influence respiration and, therefore, lead to false interpretation of data if not accounted for in the design. Scalable in vivo variables that influence respiratory control may not be captured in all HRR-protocols.…”

“…However, by using the complex I specific inhibitor, rotenone, which abolished these differences, we were able to conclude that hydrogen peroxide constrains respiration specific to mitochondrial complex I. Using a similar SUIT protocol, Davis and Barrett examined the effects of exercise training on Alaskan sled dog skeletal muscle mitochondrial respiration 39 . They observed a significant effect of exercise training on complex I and II respiration at various temperatures 39 .…”

“…Using a similar SUIT protocol, Davis and Barrett examined the effects of exercise training on Alaskan sled dog skeletal muscle mitochondrial respiration 39 . They observed a significant effect of exercise training on complex I and II respiration at various temperatures 39 . However, upon addition of rotenone the differences were eliminated suggesting that the effects of exercise primarily improve complex I function in this impressive model of mitochondrial function 39 …”

Biomarkers of heatstroke‐induced organ injury and repair

“…A specific role for mitochondria in heat‐induced muscle injury is suggested by the fact that lesions induced by passive heating are more prominent in muscles with higher oxidative capacity (Sharma et al., 2021). Increased temperature has been shown to increase mitochondrial leak respiration in skeletal muscle in rats (Jarmuszkiewicz et al., 2015), dogs (Davis & Barrett, 2021), horses (Davis et al., 2020) and humans (Fiorenza et al., 2019). Increased leak respiration will decrease the efficiency of ATP synthesis and as a result increased heat production through oxidative metabolism is necessary to maintain the desired rate of ATP synthesis.…”