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Cytochrome oxidase activity of mitochondria from ischemic and reperfused myocardium
Abstract:
Polarographic measurements show that activity of cytochrome oxidase (CO), assayed as ascorbate plus TMPD oxidase, is decreased in the mitochondria (M) from postischemic areas of rabbit heart 1, 6, and 9 days after temporary (1-hr) coronary artery occlusion (CAO). This effect is observable only in the absence of added cytochrome c. Cytochrome oxidase activity in the cytochrome c-containing medium was not different from the control level. Levels of cytochromes c + c1 and a were substantially lower in tissue from postischemic areas and elevated in the intact tissue 1 and 6 days after temporary CAO as compared with control hearts. Stoichiometry of the cytochromes was not changed. After 1 or 4 hr of permanent CAO, CO activity (plus cytochrome c) of ischemic M was equal to that of M from intact area; CO activity (with or without cytochrome c) was reduced after 0.5 and 1 hr but elevated after 3 or 4 hr of in vitro ischemia as compared with control. The changes of CO activity in infarcted human heart M were similar to those in rabbits after temporary CAO; CO activity was restored after addition of cytochrome c. The data suggest that leakage of cytochrome c occurs during isolation of M and is more pronounced in ischemia-damaged M.
Insights
Mitochondrial cytochrome oxidase activity decreases after heart ischemia, especially when cytochrome c is depleted. This suggests cytochrome c leakage from damaged mitochondria, impacting heart function recovery.
Area of Science:
- Cardiovascular Physiology
- Mitochondrial Function
- Ischemic Heart Disease
Background:
- Coronary artery occlusion (CAO) leads to myocardial ischemia, affecting cellular energy production.
- Cytochrome oxidase (CO) is a key enzyme in the mitochondrial electron transport chain, crucial for ATP synthesis.
- Previous studies indicate altered mitochondrial function post-ischemia, but the specific role of CO and cytochrome c is not fully elucidated.
Purpose of the Study:
- To investigate the activity of cytochrome oxidase (CO) in mitochondria following temporary and permanent coronary artery occlusion (CAO).
- To determine the impact of cytochrome c availability on CO activity in post-ischemic heart mitochondria.
- To assess changes in cytochrome levels in ischemic and non-ischemic heart tissues.
Main Methods:
- Polarographic measurements were used to assay CO activity in heart mitochondria isolated from rabbits after temporary (1-hr) CAO.
- CO activity was measured with and without the addition of exogenous cytochrome c.
- Cytochrome levels (c+c1 and a) in heart tissue were quantified using spectrophotometry.
- In vitro ischemia models were used to study CO activity in mitochondria subjected to varying durations of oxygen deprivation.
Main Results:
- Mitochondrial CO activity was decreased in post-ischemic rabbit heart areas 1, 6, and 9 days after temporary CAO, particularly when exogenous cytochrome c was omitted.
- CO activity was restored to control levels upon addition of cytochrome c, indicating cytochrome c deficiency in isolated mitochondria.
- Tissue levels of cytochromes c+c1 and a were reduced in post-ischemic areas and elevated in intact areas after temporary CAO.
- In vitro ischemia showed reduced CO activity at early time points (0.5-1 hr) but elevated activity at later time points (3-4 hr).
- Similar CO activity restoration with cytochrome c was observed in infarcted human heart mitochondria.
Conclusions:
- Ischemia-induced damage leads to a pronounced leakage of cytochrome c from heart mitochondria during isolation.
- The observed decrease in CO activity post-ischemia is primarily due to cytochrome c deficiency rather than intrinsic enzyme dysfunction.
- Restoration of CO activity upon cytochrome c addition highlights the critical role of cytochrome c availability in mitochondrial respiration after ischemic injury.
- These findings have implications for understanding the mechanisms of cardiac dysfunction and recovery following ischemic events.