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Production of reactive oxygen by mitochondria from normoxic and hypoxic rat heart tissue
T Paraidathathu1, H de Groot, J P Kehrer
1Division of Pharmacology and Toxicology, College of Pharmacy, University of Texas, Austin 78712-1074.
Abstract:
Reactive oxygen species (ROS), which may be involved in ischemic or reperfusion heart injury, can be produced by mitochondria. Previous work indicated that coupled mitochondria from ischemic heart tissue incubated in calcium-free medium produced less ROS than normal. The effects of calcium, which may be elevated in hypoxic or ischemic tissue, were not examined. The relative production of ROS by mitochondria from normoxic or hypoxic rat heart tissue was estimated by measuring the oxidation of dichlorofluorescin to the fluorescent compound, dichlorofluorescein. ROS were detectable during succinate-stimulated State 4 respiration. In the absence of calcium, mitochondria from hypoxic (60 min) heart tissue produced less ROS than mitochondria from normoxic heart tissue. In the presence of 0.1, 1 or 10 microM calcium, ROS produced by hypoxic mitochondria were increased to normoxic levels. While function was depressed in mitochondria from hypoxic tissue, the presence of 0.1 and 1 microM calcium had no further effect. Respiration was uncoupled in the presence of 10 microM calcium in mitochondria from both normoxic and hypoxic heart tissue. ROS production was increased in mitochondria from hypoxic tissue with both increasing concentrations of calcium and increasing duration of exposure. ROS production in mitochondria from normoxic heart tissue was only stimulated after 200 or more seconds of exposure to 1 or 10 microM calcium. Production of ROS in mitochondria from hypoxic tissue in the presence of 1 microM calcium was inhibited by rotenone (80%), ruthenium red (69%), and a combination of these agents (96%). In contrast, ruthenium red had no effect on ROS production by mitochondria from normoxic heart tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Calcium influences mitochondrial reactive oxygen species (ROS) production in heart tissue. Hypoxic heart mitochondria produce less ROS, but calcium can restore levels, impacting heart injury research.
Area of Science:
- Mitochondrial biochemistry
- Cardiovascular research
- Oxidative stress
Background:
- Mitochondria produce reactive oxygen species (ROS), implicated in heart injury.
- Previous studies showed reduced ROS from ischemic heart mitochondria in calcium-free conditions.
- The role of calcium, often elevated in hypoxia/ischemia, was unexamined.
Purpose of the Study:
- To investigate the effect of calcium on ROS production by mitochondria from normoxic and hypoxic rat hearts.
- To understand calcium's role in modulating mitochondrial ROS during cardiac stress.
Main Methods:
- Mitochondrial ROS production was measured using dichlorofluorescin oxidation.
- Experiments involved normoxic and hypoxic rat heart mitochondria.
- Varying calcium concentrations (0.1-10 microM) and exposure durations were tested.
Main Results:
- Hypoxic mitochondria produced less ROS without calcium; calcium restored levels.
- Higher calcium (10 microM) uncoupled respiration in both normoxic and hypoxic mitochondria.
- ROS production in hypoxic mitochondria increased with calcium concentration and exposure time.
Conclusions:
- Calcium plays a significant role in modulating mitochondrial ROS production during cardiac hypoxia.
- Understanding calcium-ROS interactions is crucial for addressing ischemic/reperfusion heart injury.
- Mitochondrial ROS production is sensitive to calcium levels and duration of exposure in hypoxic conditions.