title: Tissue and sex specificities in Ca2+ handling by isolated mitochondria in conditions avoiding the permeability transition.
abstract: What is the central question of this study? The assessment of Ca(2+) handling by isolated mitochondria can be biased by dysfunctions secondary to Ca(2+) -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 Ca(2+) transport are still unsettled questions. What is the main finding and its importance? If MPT is not prevented during Ca(2+) transport assays, some measured variables are biased. Accounting for the implied importance of preventing MPT, we observed substantial tissue specificities in the mitochondrial Ca(2+) handling, particularly in the Ca(2+) efflux pathways. The characteristics of mitochondria, including their Ca(2+) transport functions, may exhibit tissue specificity and sexual dimorphism. Given that measurements of Ca(2+) handling by isolated mitochondria may be biased by dysfunction secondary to Ca(2+) -induced mitochondrial permeability transition (MPT) pore opening, this study evaluated the extent to which MPT inhibition by ciclosporin affected the measurement of Ca(2+) transport in isolated rat liver mitochondria. The results indicate that the steady-state levels of external Ca(2+) and the rates of mitochondrial Ca(2+) efflux through the selective pathways can be overestimated by up to fourfold if MPT pore opening is not prevented. We analysed Ca(2+) 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 Ca(2+), Mg(2+) and Na(+). The Ca(2+) influx rates were similar among the samples, except that the liver mitochondria displayed values fourfold higher. In contrast, the Ca(2+) efflux rates exhibited more tissue diversity, especially in the presence of Na(+). Interestingly, the Na(+)-independent Ca(2+) efflux was highest in the heart mitochondria (∼ 4 nmol mg(-1) min(-1)), thus challenging the view that cardiac mitochondrial Ca(2+) efflux relies almost exclusively on a Na(+)-dependent pathway. Sex specificity was observed in only two kinetic indexes of heart mitochondrial Ca(2+) 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 Ca(2+) handling by isolated mitochondria.
authors.affiliation: Department of Clinical Pathology, Faculty of Medical Sciences, State University of Campinas, Campinas, Brazil.
authors.forename: Hanan
authors.initials: H
authors.lastname: Chweih
authors.affiliation: Department of Clinical Pathology, Faculty of Medical Sciences, State University of Campinas, Campinas, Brazil.
authors.forename: Roger F
authors.initials: RF
authors.lastname: Castilho
authors.forename: Tiago R
authors.initials: TR
authors.lastname: Figueira
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005260:Female; D006706:Homeostasis / Q000502:physiology; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008929:Mitochondria, Heart / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D008933:Mitochondrial Swelling / Q000502:physiology; D010539:Permeability; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D012964:Sodium; D008274:Magnesium; D002118:Calcium