How does calcium regulate mitochondrial energetics in the heart? - new insights

Mitochondrial dysfunction in heart diseases: Potential therapeutic effects of Panax ginseng

Heart diseases have a high incidence and mortality rate, and seriously affect people's quality of life. Mitochondria provide energy for the heart to function properly. The process of various heart diseases is closely related to mitochondrial dysfunction. Panax ginseng (P. ginseng), as a traditional Chinese medicine, is widely used to treat various cardiovascular diseases. Many studies have confirmed that P. ginseng and ginsenosides can regulate and improve mitochondrial dysfunction. Therefore, the role of mitochondria in various heart diseases and the protective effect of P. ginseng on heart diseases by regulating mitochondrial function were reviewed in this paper, aiming to gain new understanding of the mechanisms, and promote the clinical application of P. ginseng.

Effect of Exogenous Electric Stimulation on the Cardiac Tissue Function In Situ Monitored by Scanning Electrochemical Microscopy

Cardiac tissue is sensitive to and can be easily damaged by exogenous electric stimulation. However, due to the thermal-electric coeffect and the limitation of in situ and quantitative information on the cardiac tissue function under electric stimulation, the detailed effect and the underlying mechanism of exogenous electric stimulation on the cardiac tissue remain elusive. To address this, in this work, we first constructed an in vitro cardiac tissue model and established a thermal-electric coupled theoretical model for simulating the electric field and temperature distributions around the cardiac tissue, from which we selected the electric field strengths (1.19, 2.37, and 3.39 kV cm^-1) and electrical energies (0.001, 0.005, and 0.011 J) for electric stimulations without inducing a thermal effect. Then, we applied electric field stimulations on the cardiac tissue using these parameters and scanning electrochemical microscopy (SECM) to in situ and quantitatively monitor the dynamic changes in the key parameters of the cardiac tissue function, including respiratory activity, membrane permeability, and contraction frequency, after electric field stimulations. The SECM results showed that the oxygen consumption, cell membrane permeability coefficient, and contraction frequency of the cardiac tissue were strongly dependent on electrical energy, especially when the electrical energy was higher than 0.001 J. Our work, for the first time, achieves the in situ and quantitative monitoring of the cardiac tissue function under electric stimulation using SECM, which would provide important references for designing an electric stimulation regime for cardiac tissue engineering and clinical application of electrotherapy.

Resveratrol Carbon Dots Disrupt Mitochondrial Function in Cancer Cells

Resveratrol, a natural polyphenol, exhibits beneficial health properties and has been touted as a potential anti-tumor agent. Here, we demonstrate potent anti-cancer effects of carbon dots (C-dots) synthesized from resveratrol. The mild synthesis conditions retained resveratrol functional moieties upon the carbon dots' (C-dots) surface, an important requisite for achieving specificity toward cancer cells and biological activities. Indeed, the disruptive effects of the resveratrol-C-dot were more pronounced in several cancer cell types compared to normal cells, underscoring targeting capabilities of the C-dots, a pertinent issue for the development of cancer therapeutics. In particular, we observed impairment of mitochondrial functionalities, including intracellular calcium release, inhibition of cytochrome-C oxidase enzyme activity, and mitochondrial membrane perturbation. Furthermore, the resveratrol C-dots were more potent than either resveratrol molecules alone, known anti-cancer polyphenolic agents such as curcumin and triphenylphosphonium, or C-dots prepared from different carbonaceous precursors. This study suggests that resveratrol-synthesized C-dots may have promising therapeutic potential as anti-cancer agents.

Mitochondrial Ca2+ Homeostasis: Emerging Roles and Clinical Significance in Cardiac Remodeling

Mitochondria are the sites of oxidative metabolism in eukaryotes where the metabolites of sugars, fats, and amino acids are oxidized to harvest energy. Notably, mitochondria store Ca²⁺ and work in synergy with organelles such as the endoplasmic reticulum and extracellular matrix to control the dynamic balance of Ca²⁺ concentration in cells. Mitochondria are the vital organelles in heart tissue. Mitochondrial Ca²⁺ homeostasis is particularly important for maintaining the physiological and pathological mechanisms of the heart. Mitochondrial Ca²⁺ homeostasis plays a key role in the regulation of cardiac energy metabolism, mechanisms of death, oxygen free radical production, and autophagy. The imbalance of mitochondrial Ca²⁺ balance is closely associated with cardiac remodeling. The mitochondrial Ca²⁺ uniporter (mtCU) protein complex is responsible for the uptake and release of mitochondrial Ca²⁺ and regulation of Ca²⁺ homeostasis in mitochondria and consequently, in cells. This review summarizes the mechanisms of mitochondrial Ca²⁺ homeostasis in physiological and pathological cardiac remodeling and the regulatory effects of the mitochondrial calcium regulatory complex on cardiac energy metabolism, cell death, and autophagy, and also provides the theoretical basis for mitochondrial Ca²⁺ as a novel target for the treatment of cardiovascular diseases.

Melatonin fine-tunes intracellular calcium signals and eliminates myocardial damage through the IP3R/MCU pathways in cardiorenal syndrome type 3

Cardiorenal syndrome type-3 (CRS-3) is characterized by acute cardiac injury induced by acute kidney injury. Here, we investigated the causes of CRS-3 by analyzing cardiac function after renal ischemia-reperfusion injury (IRI) using echocardiography and evaluation of pro-inflammatory markers, calcium balance, mitochondrial function, and cardiomyocyte death. Our results show that renal IRI reduces cardiac diastolic function associated with cardiomyocyte death and inflammatory responses. Renal IRI also disrupts cardiomyocyte energy metabolism, induces calcium overload, and impairs mitochondrial function, as evidenced by reduced mitochondrial membrane potential and increased mitochondrial fission. Further, renal IRI induces phosphorylation of inositol 1,4,5-trisphosphate receptor (IP3R) and expression of mitochondrial calcium uniporter (MCU), resulting in cytoplasmic calcium overload and mitochondrial calcium accumulation. Pretreatment with melatonin attenuates renal IRI-mediated cardiac damage by maintaining myocardial diastolic function and reducing cardiomyocyte death. Melatonin also inhibits IP3R phosphorylation and MCU expression, thereby alleviating cytoplasmic and mitochondrial calcium overload. Blockade of IP3R has similar cardioprotective effects, whereas MCU activation abrogates the melatonin-mediated cardioprotection. These results show that the negative effects of renal IRI on myocardial viability and cardiac function are caused by induced IP3R phosphorylation, MCU upregulation, and calcium overload. Melatonin protects cardiac function against CRS-3 by suppressing IP3R-MCU signaling.

Crosstalk between Mitochondria and Cytoskeleton in Cardiac Cells

Elucidation of the mitochondrial regulatory mechanisms for the understanding of muscle bioenergetics and the role of mitochondria is a fundamental problem in cellular physiology and pathophysiology. The cytoskeleton (microtubules, intermediate filaments, microfilaments) plays a central role in the maintenance of mitochondrial shape, location, and motility. In addition, numerous interactions between cytoskeletal proteins and mitochondria can actively participate in the regulation of mitochondrial respiration and oxidative phosphorylation. In cardiac and skeletal muscles, mitochondrial positions are tightly fixed, providing their regular arrangement and numerous interactions with other cellular structures such as sarcoplasmic reticulum and cytoskeleton. This can involve association of cytoskeletal proteins with voltage-dependent anion channel (VDAC), thereby, governing the permeability of the outer mitochondrial membrane (OMM) to metabolites, and regulating cell energy metabolism. Cardiomyocytes and myocardial fibers demonstrate regular arrangement of tubulin beta-II isoform entirely co-localized with mitochondria, in contrast to other isoforms of tubulin. This observation suggests the participation of tubulin beta-II in the regulation of OMM permeability through interaction with VDAC. The OMM permeability is also regulated by the specific isoform of cytolinker protein plectin. This review summarizes and discusses previous studies on the role of cytoskeletal proteins in the regulation of energy metabolism and mitochondrial function, adenosine triphosphate (ATP) production, and energy transfer.

Impaired calcium handling and mitochondrial metabolic dysfunction as early markers of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder, characterised by myocyte remodeling, disorganisation of sarcomeric proteins, impaired energy metabolism and altered cardiac contractility. Gene mutations encoding cardiac contractile proteins account for 60% of HCM aetiology. Current drug therapy including L-type calcium channel antagonists, are used to manage symptoms in patients with overt HCM, but no treatment exists that can reverse or prevent the cardiomyopathy. Design of effective drug therapy will require a clear understanding of the early pathophysiological mechanisms of the disease. Numerous studies have investigated specific aspects of HCM pathophysiology. This review brings these findings together, in order to develop a holistic understanding of the early pathophysiological mechanisms of the disease. We focus on gene mutations in cardiac myosin binding protein-C, β-cardiac myosin heavy chain, cardiac troponin I, and cardiac troponin T, that comprise the majority of all HCM sarcomeric gene mutations. We find that although some similarities exist, each mutation leads to mutation-specific alterations in calcium handling, myofilament calcium sensitivity and mitochondrial metabolic function. This may contribute to the observed clinical phenotypic variability in sarcomeric-related HCM. An understanding of early mutation-specific mechanisms of the disease may provide useful markers of disease progression, and inform therapeutic design.

Mitochondrial calcium uptake in organ physiology: from molecular mechanism to animal models

Mitochondrial Ca²⁺ is involved in heterogeneous functions, ranging from the control of metabolism and ATP production to the regulation of cell death. In addition, mitochondrial Ca²⁺ uptake contributes to cytosolic [Ca²⁺] shaping thus impinging on specific Ca²⁺-dependent events. Mitochondrial Ca²⁺ concentration is controlled by influx and efflux pathways: the former controlled by the activity of the mitochondrial Ca²⁺ uniporter (MCU), the latter by the Na⁺/Ca²⁺ exchanger (NCLX) and the H⁺/Ca²⁺ (mHCX) exchanger. The molecular identities of MCU and of NCLX have been recently unraveled, thus allowing genetic studies on their physiopathological relevance. After a general framework on the significance of mitochondrial Ca²⁺ uptake, this review discusses the structure of the MCU complex and the regulation of its activity, the importance of mitochondrial Ca²⁺ signaling in different physiological settings, and the consequences of MCU modulation on organ physiology.

The cardiac L-type calcium channel alpha subunit is a target for direct redox modification during oxidative stress-the role of cysteine residues in the alpha interacting domain

Cardiovascular disease is the leading cause of death in the Western world. The incidence of cardiovascular disease is predicted to further rise with the increase in obesity and diabetes and with the aging population. Even though the survival rate from ischaemic heart disease has improved over the past 30 years, many patients progress to a chronic pathological condition, known as cardiac hypertrophy that is associated with an increase in morbidity and mortality. Reactive oxygen species (ROS) and calcium play an essential role in mediating cardiac hypertrophy. The L-type calcium channel is the main route for calcium influx into cardiac myocytes. There is now good evidence for a direct role for the L-type calcium channel in the development of cardiac hypertrophy. Cysteines on the channel are targets for redox modification and glutathionylation of the channel can modulate the function of the channel protein leading to the onset of pathology. The cysteine responsible for modification of L-type calcium channel function has now been identified. Detailed understanding of the role of cysteines as possible targets during oxidative stress may assist in designing therapy to prevent the development of hypertrophy and heart failure.

Dystrophic Cardiomyopathy-Potential Role of Calcium in Pathogenesis, Treatment and Novel Therapies

Duchenne muscular dystrophy (DMD) is caused by defects in the DMD gene and results in progressive wasting of skeletal and cardiac muscle due to an absence of functional dystrophin. Cardiomyopathy is prominent in DMD patients, and contributes significantly to mortality. This is particularly true following respiratory interventions that reduce death rate and increase ambulation and consequently cardiac load. Cardiomyopathy shows an increasing prevalence with age and disease progression, and over 95% of patients exhibit dilated cardiomyopathy by the time they reach adulthood. Development of the myopathy is complex, and elevations in intracellular calcium, functional muscle ischemia, and mitochondrial dysfunction characterise the pathophysiology. Current therapies are limited to treating symptoms of the disease and there is therefore an urgent need to treat the underlying genetic defect. Several novel therapies are outlined here, and the unprecedented success of phosphorodiamidate morpholino oligomers (PMOs) in preclinical and clinical studies is overviewed.

The L-type Ca(2+) channel facilitates abnormal metabolic activity in the cTnI-G203S mouse model of hypertrophic cardiomyopathy

KEY POINTS

Genetic mutations in cardiac troponin I (cTnI) are associated with development of hypertrophic cardiomyopathy characterized by myocyte remodelling, disorganization of cytoskeletal proteins and altered energy metabolism. The L-type Ca(2+) channel is the main route for calcium influx and is crucial to cardiac excitation and contraction. The channel also regulates mitochondrial function in the heart by a functional communication between the channel and mitochondria via the cytoskeletal network. We find that L-type Ca(2+) channel kinetics are altered in cTnI-G203S cardiac myocytes and that activation of the channel causes a significantly greater increase in mitochondrial membrane potential and metabolic activity in cTnI-G203S cardiac myocytes. These responses occur as a result of impaired communication between the L-type Ca(2+) channel and cytoskeletal protein F-actin, involving decreased movement of actin-myosin and block of the mitochondrial voltage-dependent anion channel, resulting in a 'hypermetabolic' mitochondrial state. We propose that L-type Ca(2+) channel antagonists, such as diltiazem, might be effective in reducing the cardiomyopathy by normalizing mitochondrial metabolic activity.

ABSTRACT

Genetic mutations in cardiac troponin I (cTnI) account for 5% of families with hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy is associated with disorganization of cytoskeletal proteins and altered energy metabolism. The L-type Ca(2+) channel (ICa-L ) plays an important role in regulating mitochondrial function. This involves a functional communication between the channel and mitochondria via the cytoskeletal network. We investigate the role of ICa-L in regulating mitochondrial function in 25- to 30-week-old cardiomyopathic mice expressing the human disease-causing mutation Gly203Ser in cTnI (cTnI-G203S). The inactivation rate of ICa-L is significantly faster in cTnI-G203S myocytes [cTnI-G203S: τ1  = 40.68 ± 3.22, n = 10 vs. wild-type (wt): τ1  = 59.05 ± 6.40, n = 6, P < 0.05]. Activation of ICa-L caused a greater increase in mitochondrial membrane potential (Ψm , 29.19 ± 1.85%, n = 15 vs. wt: 18.84 ± 2.01%, n = 10, P < 0.05) and metabolic activity (24.40 ± 6.46%, n = 8 vs. wt: 9.98 ± 1.57%, n = 9, P < 0.05). The responses occurred because of impaired communication between ICa-L and F-actin, involving lack of dynamic movement of actin-myosin and block of the mitochondrial voltage-dependent anion channel. Similar responses were observed in precardiomyopathic mice. ICa-L antagonists nisoldipine and diltiazem decreased Ψm to basal levels. We conclude that the Gly203Ser mutation leads to impaired functional communication between ICa-L and mitochondria, resulting in a 'hypermetabolic' state. This might contribute to development of cTnI-G203S cardiomyopathy because the response is present in young precardiomyopathic mice. ICa-L antagonists might be effective in reducing the cardiomyopathy by altering mitochondrial function.

Inhibitory effect of progesterone during early embryonic development: Suppression of myocardial differentiation and calcium-related transcriptome by progesterone in mESCs: Progesterone disturb cardiac differentiation of mESCs through lower cytosolic Ca(2.)

Progesterone (PG) and its derivates are used in prevention of spontaneous miscarriage. However, some studies have reported that exposure to PG and its derivates during pregnancy can cause malformations and affect both blood pressure and the cardiovascular system. The effect of PG on cardiomyogenesis of mouse embryonic stem cells (mESCs) is not well known. Expression of Pgr mRNA showed an opposite pattern of beating-ratio during differentiation. PG treatment resulted in reduction of the beating ratio to 60.45±1.54% from 92.17±2.98% in normal differentiation, reduced transcripts of heart morphogenesis and Ca(2+) binding-related genes in the next generation sequencing data and significantly decreased expression levels of Ca(2+)/contraction-related genes including Ryr2, Calm2, Trpv2, and Mylk3, the intracellular Ca(2+) level, and the beating frequency. These results suggest that PG exerts inhibitory effects on differentiation of mESCs into functional cardiomyocytes.

The Role of the L-Type Ca2+ Channel in Altered Metabolic Activity in a Murine Model of Hypertrophic Cardiomyopathy

Heterozygous mice (αMHC^403/+) expressing the human disease-causing mutation Arg403Gln exhibit cardinal features of hypertrophic cardiomyopathy (HCM) including hypertrophy, myocyte disarray, and increased myocardial fibrosis. Treatment of αMHC^403/+mice with the L-type calcium channel (I_Ca-L) antagonist diltiazem has been shown to decrease left ventricular anterior wall thickness, cardiac myocyte hypertrophy, disarray, and fibrosis. However, the role of the I_Ca-L in the development of HCM is not known. In addition to maintaining cardiac excitation and contraction in myocytes, the I_Ca-L also regulates mitochondrial function through transmission of movement of I_Ca-L via cytoskeletal proteins to mitochondrial voltage-dependent anion channel. Here, the authors investigated the role of I_Ca-L in regulating mitochondrial function in αMHC^403/+mice. Whole-cell patch clamp studies showed that I_Ca-L current inactivation kinetics were significantly increased in αMHC^403/+cardiac myocytes, but that current density and channel expression were similar to wild-type cardiac myocytes. Activation of I_Ca-L caused a significantly greater increase in mitochondrial membrane potential and metabolic activity in αMHC^403/+. These increases were attenuated with I_Ca-L antagonists and following F-actin or β-tubulin depolymerization. The authors observed increased levels of fibroblast growth factor-21 in αMHC^403/+mice, and altered mitochondrial DNA copy number consistent with altered mitochondrial activity and the development of cardiomyopathy. These studies suggest that the Arg403Gln mutation leads to altered functional communication between I_Ca-L and mitochondria that is associated with increased metabolic activity, which may contribute to the development of cardiomyopathy. I_Ca-L antagonists may be effective in reducing the cardiomyopathy in HCM by altering metabolic activity.

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Heterozygous mice (αMHC^403/+) expressing the human hypertrophic cardiomyopathy (HCM) disease causing mutation Arg403Gln exhibit cardinal features of HCM.

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This study investigated the role of L-type Ca2+ channel (ICa-L) in regulating mitochondrial function in Arg403Gln (αMHC^403/+) mice.

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Activation of ICa-L in αMHC^403/+mice caused a significantly greater increase in mitochondrial membrane potential and metabolic activity when compared to wild-type mice.

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Increases in mitochondrial membrane potential and metabolic activity were attenuated with ICa-L antagonists and when F-actin or β-tubulin were depolymerized.

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ICa-L antagonists may be effective in reducing the cardiomyopathy in HCM by altering metabolic activity.

Integrated microRNA and mRNA responses to acute human left ventricular ischemia

MicroRNAs (miRNAs) play a significant role in ischemic heart disease. Animal models of left ventricular (LV) ischemia demonstrate a unique miRNA profile; however, these models have limitations in describing human disease. In this study, we performed next-generation miRNA and mRNA sequencing on LV tissue from nine patients undergoing cardiac surgery with cardiopulmonary bypass and cardioplegic arrest. Samples were obtained immediately after aortic cross clamping (baseline) and before aortic cross clamp removal (postischemic). Of 1,237 identified miRNAs, 21 were differentially expressed between baseline and postischemic LV samples including the upregulated miRNAs miR-339-5p and miR-483-3p and the downregulated miRNA miR-139-5p. Target prediction analysis of these miRNAs was integrated with mRNA expression from the same LV samples to identify anticorrelated miRNA-mRNA pairs. Gene enrichment studies of candidate mRNA targets demonstrated an association with cardiovascular disease, cell death, and metabolism. Therapeutics that intervene on these miRNAs and their downstream targets may lead to novel mechanisms of mitigating the damage caused by ischemic insults on the human heart.

What is the function of mitochondrial networks? A theoretical assessment of hypotheses and proposal for future research

Mitochondria can change their shape from discrete isolated organelles to a large continuous reticulum. The cellular advantages underlying these fused networks are still incompletely understood. In this paper, we describe and compare hypotheses regarding the function of mitochondrial networks. We use mathematical and physical tools both to investigate existing hypotheses and to generate new ones, and we suggest experimental and modelling strategies. Among the novel insights we underline from this work are the possibilities that (i) selective mitophagy is not required for quality control because selective fusion is sufficient; (ii) increased connectivity may have non-linear effects on the diffusion rate of proteins; and (iii) fused networks can act to dampen biochemical fluctuations. We hope to convey to the reader that quantitative approaches can drive advances in the understanding of the physiological advantage of these morphological changes.

Dysregulated Ca2+ homeostasis in Fanconi anemia cells

Fanconi Anemia (FA) is a rare and complex inherited blood disorder associated with bone marrow failure and malignancies. Many alterations in FA physiology appear linked to red-ox unbalance including alterations in the morphology and structure of nuclei, intermediate filaments and mitochondria, defective respiration, reduced ATP production and altered ATP/AMP ratio. These defects are consistently associated with impaired oxygen metabolism indeed treatment with antioxidants N-acetylcysteine (NAC) and resveratrol (RV) does rescue FA physiology. Due to the importance of the intracellular calcium signaling and its key function in the control of intracellular functions we were interested to study calcium homeostasis in FA. We found that FANCA cells display a dramatically low intracellular calcium concentration ([Ca²⁺]_i) in resting conditions. This condition affects cellular responses to stress. The flux of Ca²⁺ mobilized by H₂O₂ from internal stores is significantly lower in FANCA cells in comparison to controls. The low basal [Ca²⁺]_i in FANCA appears to be an actively maintained process controlled by a finely tuned interplay between different intracellular Ca²⁺ stores. The defects associated with the altered Ca²⁺ homeostasis appear consistently overlapping those related to the unbalanced oxidative metabolism in FA cells underlining a contiguity between oxidative stress and calcium homeostasis.

Nanoparticle-mediated dual delivery of an antioxidant and a peptide against the L-Type Ca2+ channel enables simultaneous reduction of cardiac ischemia-reperfusion injury

Increased reactive oxygen species (ROS) production and elevated intracellular Ca(2+) following cardiac ischemia-reperfusion injury are key mediators of cell death and the development of cardiac hypertrophy. The L-type Ca(2+) channel is the main route for calcium influx in cardiac myocytes. Activation of the L-type Ca(2+) channel leads to a further increase in mitochondrial ROS production and metabolism. We have previously shown that the application of a peptide derived against the alpha-interacting domain of the L-type Ca(2+) channel (AID) decreases myocardial injury post reperfusion. Herein, we examine the efficacy of simultaneous delivery of the AID peptide in combination with the potent antioxidants curcumin or resveratrol using multifunctional poly(glycidyl methacrylate) (PGMA) nanoparticles. We highlight that drug loading and dissolution are important parameters that have to be taken into account when designing novel combinatorial therapies following cardiac ischemia-reperfusion injury. In the case of resveratrol low loading capacity and fast release rates hinder its applicability as an effective candidate for simultaneous therapy. However, in the case of curcumin, high loading capacity and sustained release rates enable its effective simultaneous delivery in combination with the AID peptide. Simultaneous delivery of the AID peptide with curcumin allowed for effective attenuation of the L-type Ca(2+) channel-activated increases in superoxide (assessed as changes in DHE fluorescence; Empty NP = 53.1 ± 7.6%; NP-C-AID = 7.32 ± 3.57%) and mitochondrial membrane potential (assessed as changes in JC-1 fluorescence; Empty NP = 19.8 ± 2.8%; NP-C-AID=13.05 ± 1.78%). We demonstrate in isolated rat hearts exposed to ischemia followed by reperfusion, that curcumin and the AID peptide in combination effectively reduce muscle damage, decrease oxidative stress and superoxide production in cardiac myocytes.

Roles of Calcium Regulating MicroRNAs in Cardiac Ischemia-Reperfusion Injury

Cardiac Ca2+ cycling and signaling are closely associated with cardiac function. Changes in cellular Ca2+ homeostasis may lead to aberrant cardiac rhythm and may play a critical role in the pathogenesis of cardiac diseases, due to their exacerbation of heart failure. MicroRNAs (miRNAs) play a key role in the regulation of gene expression at the post-transcriptional level and participate in regulating diverse biological processes. The emerging evidence indicates that the expression profiles of miRNAs vary among human diseases, including cardiovascular diseases. Cardiac Ca2+-handling and signaling proteins are also regulated by miRNAs. Given the relationship between cardiac Ca2+ homeostasis and signaling and miRNA, Ca2+-related miRNAs may serve as therapeutic targets during the treatment of heart failure. In this review, we summarize the knowledge currently available regarding the role of Ca2+ in cardiac function, as well as changes in Ca2+ cycling and homeostasis and the handling of these processes by miRNAs during cardiac ischemia-reperfusion injury.