A Comparative Study of the Temperature Coefficient Q10 in Hibernating Ground Squirrels Urocitellus undulatus and Cooled Rats of Different Ages

The temperature coefficients of heart rate (Q10 _HR) oroxygen consumption (Q10 _Ox)were analyzed upon arousal from natural hibernation in long-tailedground squirrels Urocitellus undulatus andduring the rewarming of artificially precooled adult rats and ratpups. The Q10 _Ox valuewas calculated using a standard equation, whereas for calculating Q10 _HR, theequation was empirically modified to track changes in this parameterover a wide range of body temperatures (T _b).It was found that during the initial period of arousal from torpor,at T _h ≤10°C, ground squirrels demonstrated a sharp increase in the temperaturecoefficients up to Q10 _HR =40–50 and Q10 _Ox =6–7. Even higher values of Q10 _HR (>100) wererecorded at the onset of rewarming of rat pups, although they hada low level of Q10 _Ox (1.2).Adult rats could not tolerate cooling below 16°C and demonstrateda moderate variability of both Q10 _HR = 2.0–4.0and Q10 _Ox =2.0–2.2. During the recovery of normal T _b,the Q10 _HR valuesin all animals approximated to ~2.0, as predicted by the van’t Hoff–Arrheniusrule for chemical reactions in both living and inanimate nature.We assume that high values of Q10 _HR and Q10 _Ox, detectedin the early period of ground squirrel’s arousal from hibernation,may indicate the functioning of adaptive processes aimed at acceleratingbody warming. Resistance to cooling and a high Q10 _HR inrat pups may suggest the rudimentary adaptability to hibernationin the juvenile period of rats as representatives of the order Rodentia,which also includes such natural hibernators as ground squirrels.