Respiration and phosphorylation of liver mitochondria from cold-exposed rats and chipmunks

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Abstract
Comparisons were made of the effects of cold exposure on respiration and phosphorylation of liver mitochondria in rats and chipmunks. Measurements, made polarographically, indicate that the P:O ratio was unaltered in mitochondria isolated from cold-exposed rats, cold-exposed nonhibernating chipmunks and hibernating chipmunks. No differences were found in the ratio of the respiratory rate in the presence of excess substrate and adenosine diphosphate (ADP) to the respiratory rate in the presence of excess substrate only (Rs) in cold-exposed rats or in chipmunks that failed to hibernate. However, the Rs value of hibernating chipmunks was higher than that of controls. This was due to an increased substrate-ADP respiratory rate. The substrate rate (i.e., without ADP) remained unchanged. It is suggested that the increased response to ADP of mitochondria from hibernating chipmunks may be an adaptive mechanism to aid the animal in the arousal process.