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

Abstract

New Findings r 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. r 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 (ß4 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 (ß20% higher in females). The present study

The Contribution of Nicotinamide Nucleotide Transhydrogenase to Peroxide Detoxification Is Dependent on the Respiratory State and Counterbalanced by Other Sources of NADPH in Liver Mitochondria

“…Given the tissue specificity of mitochondrial characteristics (44), the results reported here may not be fully extended to mitochondria of other tissues. An organic peroxide such as t-BOOH is preferred over hydrogen peroxide, which is endogenously produced, for evaluating NADPH-supported peroxide metabolism in mitochondria because the catalase that is likely present in the isolated liver mitochondrial fraction (30) does not detoxify t-BOOH (45).…”

“…Mitochondrial Isolation and Incubation Conditions-Intact and functional mitochondria were isolated from the livers of female adult mice by differential centrifugation, as described previously (44). Measurements of oxygen consumption, the redox state of NAD(P), and the membrane potential in suspensions of intact mitochondria were performed at 28°C with continuous magnetic stirring in 2 ml of standard reaction medium (125 mM sucrose, 65 mM KCl, 2 mM KH 2 PO 4 , 1 mM MgCl 2 , 10 mM HEPES buffer, and 300 M EGTA; pH was adjusted to 7.2 with KOH).…”

Muscle metabolism and atrophy: let’s talk about sex

“…These differences appear to correspond to greater mitochondrial activities [167]. Additionally, in other tissues, such as the liver, females have greater mitochondrial content, and respiratory capacity [169,170]. Taken together, these data demonstrate that some aspects of mitochondrial quality appear inherently different between males and females, which may contribute to differential progressions of mitochondrially related pathologies including muscle atrophies ( Fig.…”

“…In aggregate, the current literature suggests inherent differences between males and females on both mitochondrial content and function [165,[167][168][169][170]. These differences may at least partially contribute to differential mitochondrial alterations during muscle pathologies and subsequent muscle loss [35,46,171].…”

“…To date, multiple studies have found mitochondrial function, morphology, and content to differ between males and females. Indeed, animal and human studies across multiple tissues have found higher mitochondrial content per gram of tissue and greater transcription factors associated with mitochondrial biogenesis in females compared to males [165,[167][168][169][170]. Female gastrocnemius muscles have greater mitochondrial content and mtDNA per gram of tissue compared to males as well as more ATP synthase, TFAM protein, and mitochondrial complexes [168].…”