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

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 $[T_{b}] = 4 C$) but distinctly nonlinear in active animals ($T_{b} = 37 C$). 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 $T_{b}'s$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...