Regulation of the rate of respiration and oxidative phosphorylation in liver mitochondria from hibernating ground squirrels, Citellus undulatus.

1. The rates of oxidation of various substrates (beta-hydroxybutyrate, succinate, ascorbate + TMPD) and the rate of ATP synthesis in liver mitochondria from active and hibernating ground squirrels were measured. 2. It was shown that the rate of mitochondrial respiration is significantly lower in hibernating animals than in active animals. 3. The degree of inhibition of mitochondrial respiration in hibernating ground squirrels was found to correlate with the length of the respiratory chain fragment involved in the oxidation of a given substrate. 4. The inhibition of mitochondrial respiration in hibernating animals was accompanied by a decrease in the rate of ATP synthesis. 5. The activity of phospholipase A2 in liver mitochondria from hibernating ground squirrels was found to be decreased. The activation of phospholipase A2 by Ca2+ ions eliminated the inhibition of respiration almost completely. 6. It was assumed that the inhibition of mitochondrial respiration during hibernation is (a) related to the suppression of phospholipase A2 activity and (b) caused by the reduced rates of electron transport through the respiratory chain and/or of substrate transport across the mitochondrial membrane.