The role of succinate dehydrogenase and oxaloacetate in metabolic suppression during hibernation and arousal |
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Authors: | Christopher Armstrong James F Staples |
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Institution: | (1) Department of Biology, University of Western Ontario, London, ON, N6A5B7, Canada; |
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Abstract: | Hibernation elicits a major reduction in whole-animal O2 consumption that corresponds with active suppression of liver mitochondrial electron transport capacity at, or downstream
of, succinate dehydrogenase (SDH). During arousal from the torpor phase of hibernation this suppression is reversed and metabolic
rates rise dramatically. In this study, we used the 13-lined ground squirrel (Ictidomys tridecemlineatus) to assess isolated liver mitochondrial respiration during the torpor phase of hibernation and various stages of arousal
to elucidate a potential role of SDH in metabolic suppression. State 3 and state 4 respiration rates were seven- and threefold
lower in torpor compared with the summer-active and interbout euthermic states. Respiration rates increased during arousal
so that when body temperature reached 30°C in late arousal, state 3 and state 4 respiration were 3.3- and 1.8-fold greater
than during torpor, respectively. SDH activity was 72% higher in interbout euthermia than in torpor. Pre-incubating with isocitrate
to alleviate oxaloacetate (OAA) inhibition] increased state 3 respiration rate during torpor by 91%, but this rate was still
fourfold lower than that measured in interbout euthermia. Isocitrate pre-incubation also eliminated differences in SDH activity
among hibernation bout stages. OAA concentration correlated negatively with both respiration rates and SDH activity. These
data suggest that OAA reversibly inhibits SDH in torpor, but cannot fully account for the drastic metabolic suppression observed
during this hibernation phase. |
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