Respiratory Activity of Isolated Rat Brain Mitochondria following in vitro Exposure to Oxygen Radicals

Respiratory activity of isolated rat brain mitochondria was measured following in vitro exposure to oxygen radicals. The radicals were generated by hypoxanthine and xanthine oxidase in the presence of a suitable iron chelate and caused a severe inhibition of respiration stimulated by phosphate plus ADP (with malate + glutamate as substrate). The damage could be prevented by catalase or high concentrations of mannitol, but not by superoxide dismutase. A similar effect was observed when hypoxanthine and xanthine oxidase were replaced by glucose and glucose oxidase or by hydrogen peroxide. Most of the findings indicate that the hydroxyl radical is the damaging agent. It is concluded that brain mitochondria exposed to oxygen radicals in vitro show an inhibition of respiratory activity similar to that reported by other investigators as occurring in mitochondria in vivo following transient cerebral ischemia. Therefore, oxygen radicals may contribute to this type of cell damage.

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Influence of in vitro Lactic Acidosis and Hypercapnia on Respiratory Activity of Isolated Rat Brain Mitochondria

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/jcbfm.1984.62 ◽

1984 ◽

Vol 4 (3) ◽

pp. 430-437 ◽

Cited By ~ 102

Author(s):

Lars Hillered ◽

Lars Ernster ◽

Bo K. Siesjö

Keyword(s):

Lactic Acid ◽

Lactic Acidosis ◽

Rat Brain ◽

Mitochondrial Respiration ◽

Respiratory Activity ◽

Respiratory Control ◽

Brain Mitochondria ◽

Rat Brain Mitochondria ◽

Acid Ph ◽

Isolated Rat

Respiratory activity and the ADP/O ratio of isolated rat brain mitochondria were measured following incubation with varying concentrations of lactic acid in reaction media buffered either with bicarbonate and CO2 or with phosphate alone, at a pH of 7.1. Increasing lactic acid levels caused a progressive decrease in substrate-, phosphate-, and ADP-stimulated (State 3) respiration and ADP/O ratios. Fifteen millimolar lactic acid, pH 6.4, caused ∼50% inhibition of State 3 respiration (with malate + glutamate as substrate). At lower pH values (5.3–6.1), addition of ADP caused little or no increase in O2 consumption; i.e., ATP formation ceased. Addition of lactic acid at constant pH moderately affected respiratory control ratios but did not change State 3 respiration or ADP/O ratios. Thus, the effect of lactic acid was related to the pH change. Increasing CO2 concentrations in the reaction medium had similar effects on mitochondrial respiration, indicating that changes in extramitochondrial pH rather than in transmembrane H+ gradients determined the respiratory alterations. Following a 5-min incubation of mitochondria with lactic acid, pH 6.1, there was an incomplete recovery of State 3 respiration and respiratory control ratios. It is concluded that mitochondrial respiration is inhibited by a decrease in pH which, if excessive, may lead to a permanent suppression of ATP production. These results may, at least partly, explain the deleterious effects of enhanced lactic acidosis in brain ischemia.

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