Document Detail


Mitochondrial metabolism during daily torpor in the dwarf Siberian hamster: role of active regulated changes and passive thermal effects.
MedLine Citation:
PMID:  17804585     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
During daily torpor in the dwarf Siberian hamster, Phodopus sungorus, metabolic rate is reduced by 65% compared with the basal rate, but the mechanisms involved are contentious. We examined liver mitochondrial respiration to determine the possible role of active regulated changes and passive thermal effects in the reduction of metabolic rate. When assayed at 37 degrees C, state 3 (phosphorylating) respiration, but not state 4 (nonphosphorylating) respiration, was significantly lower during torpor compared with normothermia, suggesting that active regulated changes occur during daily torpor. Using top-down elasticity analysis, we determined that these active changes in torpor included a reduced substrate oxidation capacity and an increased proton conductance of the inner mitochondrial membrane. At 15 degrees C, mitochondrial respiration was at least 75% lower than at 37 degrees C, but there was no difference between normothermia and torpor. This implies that the active regulated changes are likely more important for reducing respiration at high temperatures (i.e., during entrance) and/or have effects other than reducing respiration at low temperatures. The decrease in respiration from 37 degrees C to 15 degrees C resulted predominantly from a considerable reduction of substrate oxidation capacity in both torpid and normothermic animals. Temperature-dependent changes in proton leak and phosphorylation kinetics depended on metabolic state; proton leakiness increased in torpid animals but decreased in normothermic animals, whereas phosphorylation activity decreased in torpid animals but increased in normothermic animals. Overall, we have shown that both active and passive changes to oxidative phosphorylation occur during daily torpor in this species, contributing to reduced metabolic rate.
Authors:
Jason C L Brown; Alexander R Gerson; James F Staples
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2007-09-05
Journal Detail:
Title:  American journal of physiology. Regulatory, integrative and comparative physiology     Volume:  293     ISSN:  0363-6119     ISO Abbreviation:  Am. J. Physiol. Regul. Integr. Comp. Physiol.     Publication Date:  2007 Nov 
Date Detail:
Created Date:  2007-11-05     Completed Date:  2007-12-26     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100901230     Medline TA:  Am J Physiol Regul Integr Comp Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  R1833-45     Citation Subset:  IM    
Affiliation:
Dept. of Biology, University of Western Ontario, London, ON, N6A 5B7, Canada.
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MeSH Terms
Descriptor/Qualifier:
Adenosine Diphosphate / metabolism
Animals
Body Temperature Regulation / physiology*
Body Weight / physiology
Citrate (si)-Synthase / metabolism
Cricetinae
Hibernation / physiology*
Kinetics
Membrane Potentials / physiology
Mitochondria, Liver / metabolism*
NADH Dehydrogenase / metabolism
Oxidation-Reduction
Oxidative Phosphorylation
Oxygen Consumption
Phodopus
Photoperiod
Succinate Cytochrome c Oxidoreductase / metabolism
Temperature*
Chemical
Reg. No./Substance:
58-64-0/Adenosine Diphosphate; EC 1.-/Succinate Cytochrome c Oxidoreductase; EC 1.6.99.3/NADH Dehydrogenase; EC 2.3.3.1/Citrate (si)-Synthase

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