Tissue and sex specificities in Ca2+ handling by isolated mitochondria in conditions avoiding the permeability transition

New Findings What is the central question of this study? The assessment of Ca2+ handling by isolated mitochondria can be biased by dysfunctions secondary to Ca2+‐induced mitochondrial permeability transition (MPT). As a result of this uncertainty and the differing experimental conditions between stu...

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Bibliographic Details
Published in:Experimental physiology 2015-09, Vol.100 (9), p.1073-1092
Main Authors: Chweih, Hanan, Castilho, Roger F., Figueira, Tiago R.
Format: Article
Language:English
Subjects:
Animals
Calcium - metabolism
Female
Homeostasis - physiology
Magnesium - metabolism
Male
Mitochondria, Heart - metabolism
Mitochondria, Liver - metabolism
Mitochondrial Membrane Transport Proteins - metabolism
Mitochondrial Permeability Transition Pore
Mitochondrial Swelling - physiology
Permeability
Rats
Rats, Wistar
Sodium - metabolism
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Summary:New Findings What is the central question of this study? The assessment of Ca2+ handling by isolated mitochondria can be biased by dysfunctions secondary to Ca2+‐induced mitochondrial permeability transition (MPT). As a result of this uncertainty and the differing experimental conditions between studies, the tissue and sex diversities in mitochondrial Ca2+ transport are still unsettled questions. What is the main finding and its importance? If MPT is not prevented during Ca2+ transport assays, some measured variables are biased. Accounting for the implied importance of preventing MPT, we observed substantial tissue specificities in the mitochondrial Ca2+ handling, particularly in the Ca2+ efflux pathways. The characteristics of mitochondria, including their Ca2+ transport functions, may exhibit tissue specificity and sexual dimorphism. Given that measurements of Ca2+ handling by isolated mitochondria may be biased by dysfunction secondary to Ca2+‐induced mitochondrial permeability transition (MPT) pore opening, this study evaluated the extent to which MPT inhibition by ciclosporin affected the measurement of Ca2+ transport in isolated rat liver mitochondria. The results indicate that the steady‐state levels of external Ca2+ and the rates of mitochondrial Ca2+ efflux through the selective pathways can be overestimated by up to fourfold if MPT pore opening is not prevented. We analysed Ca2+ transport in isolated mitochondria from the liver, skeletal muscle, heart and brain of male and female rats in incubation conditions containing MPT inhibitors, NAD‐linked substrates and relevant levels of free Ca2+, Mg2+ and Na+. The Ca2+ influx rates were similar among the samples, except that the liver mitochondria displayed values fourfold higher. In contrast, the Ca2+ efflux rates exhibited more tissue diversity, especially in the presence of Na+. Interestingly, the Na+‐independent Ca2+ efflux was highest in the heart mitochondria (∼4 nmol mg−1 min−1), thus challenging the view that cardiac mitochondrial Ca2+ efflux relies almost exclusively on a Na+‐dependent pathway. Sex specificity was observed in only two kinetic indexes of heart mitochondrial Ca2+ homeostasis and in the ADP‐stimulated respiration of liver mitochondria (∼20% higher in females). The present study shows the methodological importance of preventing MPT when measuring the properties and the physiological variability of the Ca2+ handling by isolated mitochondria.
ISSN:0958-0670
1469-445X
DOI:10.1113/EP085248