| Summary: | Hibernation in mammals is a whole‐body phenotype that involves profound reductions in metabolism and core body temperature resulting in a state of torpor. Some mammalian hibernators, such as ground squirrels, have the ability to reverse this state of hypometabolism by rewarming periodically (~every 1–4 weeks) to normothermic levels. The predominant sources of thermogenesis during these arousal periods have been shown to be brown adipose tissue (BAT) and skeletal muscle shivering. Recently, skeletal muscle non‐shivering thermogenesis has been speculated to be a significant source of heat production, which may occur via sarcolipin (SLN) uncoupling of sarcoendoplasmic reticulum (SR) calcium ATPase (SERCA)‐mediated calcium pumping. During torpor, the thermogenic contribution of BAT and skeletal muscle need to be reduced in order for hibernating mammals to maintain hypometabolic conditions. We hypothesized that skeletal muscle non‐shivering thermogenesis is a significant source of heat production and, in hibernating mammals, must be reduced during torpor. Skeletal muscle samples were taken from 2 species of ground squirrels (13‐lined and Arctic), in and out of torpor conditions, to assess fluctuations in protein expression. Preliminary results show that SLN expression is decreased during periods of torpor and significantly increase after terminal arousal from hibernation in the spring in both ground squirrel species. Furthermore, SERCA expression significantly increased during torpor in Arctic ground squirrels, which fell to normothermic levels post arousal, suggesting an enhancement of calcium handling during torpor. Next, Arctic ground squirrels were implanted with peristaltic pumps subcutaneously which delivered inhibitors of BAT‐uncoupling (SR59230A) or skeletal muscle‐uncoupling (dantrolene) during hibernation to quantify the effect of reducing specific thermogenic mechanisms directly on rewarming and metabolic rate during interbout arousals. To measure metabolic rate changes in AGS, VO 2 was monitored during ...
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