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

Abstract

The temperature coefficients of heart rate (Q10 _HR) or oxygen consumption (Q10 _Ox) were analyzed upon arousal from natural hibernation in long-tailed ground squirrels Urocitellus undulatus and during the rewarming of artificially precooled adult rats and rat pups. The Q10 _Ox value was calculated using a standard equation, whereas for calculating Q10 _HR, the equation was empirically modified to track changes in this parameter over 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 temperature coefficients up to Q10 _HR = 40–50 and Q10 _Ox = 6–7. Even higher values of Q10 _HR (>100) were recorded at the onset of rewarming of rat pups, although they had a low level of Q10 _Ox (1.2). Adult rats could not tolerate cooling below 16°C and demonstrated a moderate variability of both Q10 _HR = 2.0–4.0 and Q10 _Ox = 2.0–2.2. During the recovery of normal T _b, the Q10 _HR values in all animals approximated to ~2.0, as predicted by the van’t Hoff–Arrhenius rule for chemical reactions in both living and inanimate nature. We assume that high values of Q10 _HR and Q10 _Ox, detected in the early period of ground squirrel’s arousal from hibernation, may indicate the functioning of adaptive processes aimed at accelerating body warming. Resistance to cooling and a high Q10 _HR in rat pups may suggest the rudimentary adaptability to hibernation in the juvenile period of rats as representatives of the order Rodentia, which also includes such natural hibernators as ground squirrels.