Temperature response of oxygen uptake in brain mitochondria from normal and ischemic rats

Mitochondria isolated from rat brains following 30 min of complete (decapitation) ischemia showed a 3-fold increase in free fatty acid content, but no significant decreases in the total fatty acid or phospholipid content. This free fatty acid increase was associated with an altered mitochondrial function: a 50% inhibition of state 3 (+ ADP) respiration and a decrease in the respiratory control ratio from 5.5 to 3 to 24 degrees C. The P:O ratio remained unchanged at 3, and there was no increase in stage 4 respiration. When glutamate and malate supported respiration was determined as a function of temperature in control mitochondria, the resulting Arrhenius plot of the state 3 respiration was biphasic with a transition temperature around 30 degrees C, while ischemic mitochondria exhibited a linear Arrhenius plot with energy of activation (approximately 10 kcal/mol) similar to that of control mitochondria below the transition temperature. The difference in temperature response between control and ischemic mitochondria reflects a change in mitochondrial lipid composition, and is therefore a functional manifestation of the altered cerebral lipid composition commonly observed during ischemia.