Relationship between structure and function of liver mitochondria from hibernating and active ground squirrels, Citellus undulatus.

1. Electron microscopy of liver tissue preparations, obtained from hibernating ground squirrels, reveals mitochondria in a condensed state. 2. When kept on ice, mitochondria isolated from the livers of hibernating and active ground squirrels are in a shrunken state. 3. Incubation of mitochondria isolated from the livers of active ground squirrels in the presence of succinate, at 27 degrees C, results in mitochondrial swelling, while mitochondria from hibernating ground squirrels under the same conditions remain relatively shrunken. 4. The swollen mitochondria from active ground squirrels show high oxidative activity, while the shrunken mitochondria from hibernating animals show low oxidative activity. 5. Swelling of mitochondria from hibernating ground squirrels in a hypo-osmolar medium is accompanied by a significant increase in oxidative activity. 6. It is inferred that the shrinkage of hibernating ground squirrel mitochondria is one of the main causes of the inhibition of oxidative activity and other mitochondrial functions during hibernation.