Stoichiometry of H+ Efflux to Respiration-Dependent Ca2+ Uptake and Oxygen Consumption in Liver Mitochondria from a Hibernator

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Abstract
The initial rates of H⁺ ejection, Ca²⁺ uptake, and O₂ consumption were measured at temperatures between 4 and 37 C in liver mitochondria from Richardson's ground squirrels, Spermophilus richardsonii, in order to evaluate adaptations in bioenergetics associated with hibernation. Arrhenius plots of H⁺ ejection, Ca²⁺ uptake, and O₂ consumption were linear in hibernating animals (body temperature ) but distinctly nonlinear in active animals ( ). An average H⁺/Ca²⁺ ratio near 2 and a Ca²⁺/O ratio near 4 were observed between 4 and 37 C in both active and hibernating states, indicating a tight coupling of Ca²⁺ uptake to cellular respiration. These results suggest that the capacity for the precise regulation of cellular Ca²⁺ is retained after several weeks of hibernation at as low as 4 C. Furthermore, there does not appear to be a thermally induced disruption of the inner mitchondrial membrane in summer-active animals, since constant H⁺/Ca²⁺ and Ca²⁺/O ratios were observed at all temperatures despite an apparent dramatic change in activation energy below 21-23 C.