Seasonal changes in mitochondrial succinate dehydrogenase activity in a hibernator,Spermophilus richardsonii

Abstract

1. Liver mitochondrial functions were evaluated in Richardson's ground squirrels during different phases of the annual hibernation cycle. 2. Arrhenius plots of succinate oxidase-linked H+ ejection, Ca2+ uptake and O2 consumption exhibited discontinuities (Tc) near 21 °C in summer-active (July) ground squirrels and at 11–13 °C in warm (20 °C)- or cold (4 °C)-acclimated winter animals. No discontinuities were detected in some warm- and cold-acclimated individuals which had not yet exhibited torpor. 3. Arrhenius plots of animals killed during hibernation (Tb=4 °C) or 12–14 h after arousal from hibernation (Tb=37 °C) were linear between 4–37 °C. The rates of mitochondrial O2 consumption were markedly depressed in hibernating animals. 4. Spring (April, emerged from hibernation) animals showed a return to discontinuous Arrhenius plots with aTc near 12 °C. 5. The results indicate seasonal differences in the thermal behaviour of mitochondrial membrane functions commensurate with hibernation. The lowering of aTc in euthermic animals between summer and winter and the absence of aTc in hibernating and aroused animals suggest these seasonal changes are independent of ambient and body temperature.