Dataset Information

Calcium overload decreases net free radical emission in cardiac mitochondria.

ABSTRACT: Elevated calcium and reactive oxygen species (ROS) are responsible for the bulk of cell death occurring in a variety of clinical settings that include acute coronary events, cerebrovascular accidents, and acute kidney injury. It is commonly believed that calcium and ROS participate in a viscous cycle during these events. However, the precise feedback mechanisms are unknown. We quantitatively demonstrate in this study that, on the contrary, calcium does not stimulate free radical production but suppresses it. Isolated mitochondria from guinea pig hearts were energized with a variety of substrates and exposed to calcium concentrations designed to induce moderate calcium overload conditions associated with ischemia/reperfusion injury but do not elicit the well-known mitochondrial permeability transition phenomenon. Metabolic function and free radical emission were simultaneously quantified using high-resolution respirometry and fluorimetry. Membrane potential, high amplitude swelling, and calcium dynamics were also quantified in parallel. Our results reveal that calcium overload does not lead to excessive ROS emission but does decrease ADP stimulated respiration rates for NADH-dependent pathways. Moreover, we developed an empirical model of mitochondrial free radical homeostasis to identify the processes that are different for each substrate and calcium condition. In summary, we show that in healthy guinea pig mitochondria, calcium uptake and free radical generation do not contribute to a viscous cycle and that the relationship between net free radical production and oxygen concentration is hyperbolic. Altogether, these results lay out an important foundation necessary to quantitatively determine the role of calcium in IR injury and ROS production.

SUBMITTER: Duong QV

PROVIDER: S-EPMC7061345 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Calcium overload decreases net free radical emission in cardiac mitochondria.

Duong Quynh V QV Hoffman Adrianna A Zhong Katie K Dessinger Maria J MJ Zhang Yizhu Y Bazil Jason N JN

Mitochondrion 20200123

Elevated calcium and reactive oxygen species (ROS) are responsible for the bulk of cell death occurring in a variety of clinical settings that include acute coronary events, cerebrovascular accidents, and acute kidney injury. It is commonly believed that calcium and ROS participate in a viscous cycle during these events. However, the precise feedback mechanisms are unknown. We quantitatively demonstrate in this study that, on the contrary, calcium does not stimulate free radical production but s ...[more]

PMID: 31982614

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Project description:In neuroinflammatory and neurodegenerative disorders such as multiple sclerosis, mitochondrial damage caused by oxidative stress is believed to contribute to neuroaxonal damage. Previously, we demonstrated that exposure to hydrogen peroxide (H2O2) alters mitochondrial morphology and motility in myelinated axons and that these changes initiate at the nodes of Ranvier, where numerous sodium channels are located. Therefore, we suggested that mitochondrial damage may lead to ATP deficit, thereby affecting the efficiency of the sodium-potassium ATPase and eventually leading to sodium overload in axons. The increased intra-axonal sodium may revert the axonal sodium-calcium exchangers and thus may lead to a pathological calcium overload in the axoplasm and mitochondria. Here, we used the explanted murine ventral spinal roots to investigate whether modulation of sodium or calcium influx may prevent mitochondrial alterations in myelinated axons during exogenous application of H2O2 inducing oxidative stress. For that, tetrodotoxin, an inhibitor of voltage-gated sodium ion channels, and ruthenium 360, an inhibitor of the mitochondrial calcium uniporter, were applied simultaneously with hydrogen peroxide to axons. Mitochondrial shape and motility were analyzed. We showed that inhibition of axonal sodium influx prevented oxidative stress-induced morphological changes (i.e., increase in circularity and area and decrease in length) and preserved mitochondrial membrane potential, which is crucial for ATP production. Blocking mitochondrial calcium uptake prevented decrease in mitochondrial motility and also preserved membrane potential. Our findings indicate that alterations of both mitochondrial morphology and motility in the contexts of oxidative stress can be counterbalanced by modulating intramitochondrial ion concentrations pharmacologically. Moreover, motile mitochondria show preserved membrane potentials, pointing to a close association between mitochondrial motility and functionality.

Dataset Information

Calcium overload decreases net free radical emission in cardiac mitochondria.

Publications

Calcium overload decreases net free radical emission in cardiac mitochondria.

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