Skeletal Muscle Metabolic Enzyme Activity at Varying Temperatures in the Thirteen‐lined Ground Squirrel ( Ictidomys tridecemlineatus )

Hibernation is a prolonged season where some mammals experience a dramatic reduction in food intake while undergoing a series of torpor bouts for weeks or months at a time. During individual torpor bouts, metabolic rate decreases and hibernators will thermoconform to their environment, dropping their core body temperature (T B ) close to ambient temperature (T A ). The causality of the reduction of metabolic rate has yet to be fully understood. Thirteen lined ground squirrels, Ictidomys tridecemlineatus , endure a hibernation season of about 8 months. Although, the thirteen‐lined ground squirrels undergo hibernation for a long period of time, they still manage to preserve and maintain their organs without any greater damage and are able to achieve physiological sustainability. Given the extreme range of T B experienced throughout the hibernation period, which is unlike most other mammalian endotherms (that typically reside T B at a constant 37°C), in addition to the unique metabolic challenges of thermoregulation within and between torpor bouts, we explored function of metabolic enzymes and subsequent substrate utilization across a range of physiologic temperatures in skeletal muscle tissue. We performed functional enzyme assays of lactate dehydrogenase (LDH, marker of anaerobic metabolism) and citrate synthase (CS, marker of aerobic metabolism) in the gastrocnemius muscle from control, non‐hibernating squirrels. Preliminary LDH data suggest that anaerobic activity is higher at 37°C as compared to thermoconforming temperature ranges of 30°C and 25°C. Alternatively, preliminary CS data suggest that aerobic activity does not change across a range of physiologic temperatures. Collectively, these aerobic and anaerobic comparisons across three different physiologic temperatures suggest that squirrels may not be suppressing aerobic metabolism when thermoconforming to lower temperatures, despite overall metabolic rate suppression during torpor bouts. Future studies may look to characterizing enzyme activity at an even lower range of physiologic temperatures, and may look to include data from hibernating squirrels in addition to non‐hibernating squirrels. These kinds of preliminary baseline data can ultimately be used to better understand the physiologic basis governing reduction of metabolic rate and subsequent substrate utilization during prolonged torpor bouts. Support or Funding Information McNair Scholars Program & The College of Saint Scholastica. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .