McFarlane 2017 Am J Physiol Regul Integr Comp Physiol

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McFarlane SV, Mathers KE, Staples JF (2017) Reversible temperature-dependent differences in brown adipose tissue respiration during torpor in a mammalian hibernator. Am J Physiol Regul Integr Comp Physiol 312:R434-42.

Β» PMID: 28077390

McFarlane SV, Mathers KE, Staples JF (2017) Am J Physiol Regul Integr Comp Physiol

Abstract: Although seasonal modifications of brown adipose tissue (BAT) in hibernators are well documented, we know little about functional regulation of BAT in different phases of hibernation. In the 13-lined ground squirrel, liver mitochondrial respiration is suppressed by up to 70% during torpor. This suppression is reversed during arousal and interbout euthermia (IBE), and corresponds with patterns of maximal activities of electron transport system (ET-pathway) enzymes. Uncoupling of BAT mitochondria is controlled by free fatty acid release stimulated by sympathetic activation of adipocytes, so we hypothesized that further regulation at the level of the ET-pathway would be of little advantage. As predicted, maximal ET-pathway enzyme activities of isolated BAT mitochondria did not differ between torpor and IBE. In contrast to this pattern, respiration rates of mitochondria isolated from torpid individuals were suppressed by ~60% compared with rates from IBE individuals when measured at 37Β°C. At 10Β°C, however, mitochondrial respiration rates tended to be greater in torpor than IBE. As a result, the temperature sensitivity (Q10) of mitochondrial respiration was significantly lower in torpor (~1.4) than IBE (~2.4), perhaps facilitating energy savings during entrance into torpor and thermogenesis at low body temperatures. Despite the observed differences in isolated mitochondria, norepinephrine-stimulated respiration rates of isolated BAT adipocytes did not differ between torpor and IBE, perhaps because the adipocyte isolation requires lengthy incubation at 37Β°C, potentially reversing any changes that occur in torpor. Such changes may include remodeling of BAT mitochondrial membrane phospholipids, which could change in situ enzyme activities and temperature sensitivities.

Copyright Β© 2017 the American Physiological Society. β€’ Keywords: Q10, Electron transport system, Hibernation, Mitochondria, Uncoupled thermogenesis β€’ Bioblast editor: Kandolf G β€’ O2k-Network Lab: CA London Staples JF

Labels: MiParea: Respiration, Comparative MiP;environmental MiP 

Stress:Temperature  Organism: Other mammals  Tissue;cell: Fat  Preparation: Intact cells, Isolated mitochondria  Enzyme: Complex I, Complex II;succinate dehydrogenase, Complex III, Complex IV;cytochrome c oxidase, Complex V;ATP synthase  Regulation: Temperature  Coupling state: LEAK, ROUTINE, OXPHOS  Pathway: F, N  HRR: Oxygraph-2k 

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