Mitochondrial K+ transport and cardiac protection during ischemia/reperfusion

Ion channel-mediated mitochondrial volume regulation and its relationship with mitochondrial dynamics

The mitochondrion, one of the important cellular organelles, has the major function of generating adenosine triphosphate and plays an important role in maintaining cellular homeostasis, governing signal transduction, regulating membrane potential, controlling programmed cell death and modulating cell proliferation. The dynamic balance of mitochondrial volume is an important factor required for maintaining the structural integrity of the organelle and exerting corresponding functions. Changes in the mitochondrial volume are closely reflected in a series of biological functions and pathological changes. The mitochondrial volume is controlled by the osmotic balance between the cytoplasm and the mitochondrial matrix. Thus, any disruption in the influx of the main ion, potassium, into the cells can disturb the osmotic balance between the cytoplasm and the matrix, leading to water movement between these compartments and subsequent alterations in mitochondrial volume. Recent studies have shown that mitochondrial volume homeostasis is closely implicated in a variety of diseases. In this review, we provide an overview of the main influencing factors and research progress in the field of mitochondrial volume homeostasis.

Autosis: a new form of cell death in myocardial ischemia-reperfusion injury

Cardiomyocytes undergo a variety of cell death events during myocardial ischemia‒reperfusion injury (MIRI). Understanding the causes of cardiomyocyte mortality is critical for the prevention and treatment of MIRI. Among the various types of cell death, autosis is a recently identified type of autophagic cell death with distinct morphological and chemical characteristics. Autosis can be attenuated by autophagy inhibitors but not reversed by apoptosis or necrosis inhibitors. In recent years, it has been shown that during the late phase of reperfusion, autosis is activated, which exacerbates myocardial injury. This article describes the characteristics of autosis, autophagic cell death, and the relationship between autophagic cell death and autosis; reviews the mechanism of autosis in MIRI; and discusses its clinical significance.

Integrative analysis of transcriptome and proteome provides insights into adaptation to cadmium stress in Sedum plumbizincicola

Sedum plumbizincicola, a cadmium (Cd) hyperaccumulating herbaceous plant, can accumulate large amounts of Cd in the above-ground tissues without being poisoned. However, the molecular mechanisms regulating the processes are not fully understood. In this study, Transcriptional and proteomic analyses were integrated to investigate the response of S. plumbizincicola plants to Cd stress and to identify key pathways that are potentially responsible for Cd tolerance and accumulation. A total of 630 DAPs (differentially abundant proteins, using fold change >1.5 and adjusted p-value <0.05) were identified from Tandem Mass Tag (TMT)- based quantitative proteomic profiling, which were enriched in processes including phenylpropanoid biosynthesis, protein processing in endoplasmic reticulum, and biosynthesis of secondary metabolites. Combined with the previous transcriptomic study, 209 genes and their corresponding proteins showed the identical expression pattern. The identified genes/proteins revealed the potential roles of several metabolism pathways, including phenylpropanoid biosynthesis, oxidative phosphorylation, phagosome, and glutathione metabolism, in mediating Cd tolerance and accumulation. Lignin staining and Cd accumulation assay of the transgenic lines over-expressing a selected Cd up-regulated gene SpFAOMT (Flavonoid 3',5'-methyltransferase) showed its functions in adapting to Cd stress, and provided insight into its role in lignin biosynthesis and Cd accumulation in S. plumbizincicola during Cd stress.

Mitochondrial K+ Transport: Modulation and Functional Consequences

The existence of a K⁺ cycle in mitochondria has been predicted since the development of the chemiosmotic theory and has been shown to be crucial for several cellular phenomena, including regulation of mitochondrial volume and redox state. One of the pathways known to participate in K⁺ cycling is the ATP-sensitive K⁺ channel, MitoK_ATP. This channel was vastly studied for promoting protection against ischemia reperfusion when pharmacologically activated, although its molecular identity remained unknown for decades. The recent molecular characterization of MitoK_ATP has opened new possibilities for modulation of this channel as a mechanism to control cellular processes. Here, we discuss different strategies to control MitoK_ATP activity and consider how these could be used as tools to regulate metabolism and cellular events.

SERCA, complex I of the respiratory chain and ATP-synthase inhibition are involved in pleiotropic effects of NS1619 on endothelial cells

A large conductance potassium (BKCa) channel opener, NS1619 (1,3-dihydro-1- [2-hydroxy-5-(trifluoromethyl) phenyl]-5-(trifluoromethyl)-2H-benzimidazole-2-one), is well known for its protective effects against ischemia-reperfusion injury; however, the exact mode of its action remains unclear. The aim of this study was to characterize the effect of NS1619 on endothelial cells. The endothelial cell line EA.hy926, guinea pig hearts and submitochondrial particles isolated from the heart were used. In the isolated guinea pig hearts, which were perfused using the Langendorff technique, NS1619 caused a dose-dependent increase in coronary flow that was inhibited by L-NAME. In EA.hy926 cells, NS1619 also caused a dose-dependent increase in the intracellular calcium ion concentration [Ca(2+)]i, as measured using the FURA-2 fluorescent probe. Moreover, NS1619 decreased the oxygen consumption rate in EA.hy926 cells, as assessed using a Clark-type oxygen electrode. However, when NS1619 was applied in the presence of oligomycin, the oxygen consumption increased. NS1619 also decreased the mitochondrial membrane potential, as measured using a JC-1 fluorescent probe in the presence and absence of oligomycin. Additionally, the application of NS1619 to submitochondrial particles inhibited ATP synthase. In summary, NS1619 has pleiotropic actions on EA.hy926 cells and acts not only as an opener of the BKCa channel in EA.hy926 cells but also as an inhibitor of the respiratory chain component, sarcoplasmic reticulum ATPase, which leads to the release of Ca(2+) from the endoplasmic reticulum. Furthermore, NS1619 has the oligomycin-like property of inhibiting mitochondrial ATP synthase.

Noninvasive delayed limb ischemic preconditioning attenuates myocardial ischemia-reperfusion injury in rats by a mitochondrial K(ATP) channel-dependent mechanism

We previously demonstrated in rats that noninvasive delayed limb ischemic preconditioning (LIPC) induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb per day for three days confers the same cardioprotective effect as local ischemic preconditioning of the heart, but the mechanism has not been studied in depth. The aim of this project was to test the hypothesis that delayed LIPC enhances myocardial antioxidative ability during ischemia-reperfusion by a mitochondrial K(ATP) channel (mito K(ATP))-dependent mechanism. Rats were randomized to five groups: ischemia-reperfusion (IR)-control group, myocardial ischemic preconditioning (MIPC) group, LIPC group, IR-5HD group and LIPC-5HD group. The MIPC group underwent local ischemic preconditioning induced by three cycles of 5-min occlusion and 5-min reperfusion of the left anterior descending coronary arteries. The LIPC and LIPC-5HD groups underwent LIPC induced by three cycles of 5-min occlusion and 5-min reperfusion of the left hind limb using a modified blood pressure aerocyst per day for three days. All rats were subjected to myocardial ischemia-reperfusion injury. The IR-5HD and LIPC-5HD groups received the mito K(ATP) channel blocker 5-hydroxydecanoate Na (5-HD) before and during the myocardial ischemia-reperfusion injury. Compared with the IR-control group, both the LIPC and MIPC groups showed an amelioration of ventricular arrhythmia, reduced myocardial infarct size, increased activities of total superoxide dismutase, manganese-superoxide dismutase (Mn-SOD) and glutathione peroxidase, increased expression of Mn-SOD mRNA and decreased xanthine oxidase activity and malondialdehyde concentration. These beneficial effects of LIPC were prevented by 5-HD. In conclusion, delayed LIPC offers similar cardioprotection as local IPC. These results support the hypothesis that the activation of mito K(ATP) channels enhances myocardial antioxidative ability during ischemia-reperfusion, thereby contributing, at least in part, to the anti-arrhythmic and anti-infarct effects of delayed LIPC.

CARDIAC role of the mitochondrial Ca2+ transporters in the high-[K+](o) cardioprotection of rat hearts under ischemia and reperfusion: a mechano-energetic study

The role of mitochondrial transporters in the cardioprotection of rat hearts exposed to high [K+]-low [Ca2+]-cardioplegia (CPG) and ischemia and reperfusion (I/R) was studied through the mechano-energetic consequences of target drugs. The total heat rate (Ht) and the left intraventricular pressure (LVP) were simultaneously measured in isolated perfused hearts (30 degrees C and 1 Hz) inside a flow-calorimeter during 45 minutes of no-flow I and 45 minutes of R. After stabilization (C) they were pretreated with CPG and 100 microM 5-hydroxidecanoate (5HD, selective mKATP blocker) without and with 10 or 30 microM clonazepam (Clzp, mNCX inhibitor), 30 microM diazoxide (Dzx, selective mKATP opener), 1 microM Ru360 (selective Ca-uniporter blocker), and 0.2 microM cyclosporine-A, (mPTP inhibitor, before I and during R). Before I, 5-hydroxydecanoate in CPG increased the resting heat rate (17.83 +/- 3.55 mW/g) without changing the stunning. Clzp 30 microM + CPG + 5-hydroxydecanoate reduced the postischemic P with diastolic contracture and high Ht. Dzx protected C-hearts from stunning but increased it in CPG hearts with low economy (P/Ht) as well as Ru360. Cyclosporine-A did not modify the stunning of C or CPG ischemic hearts, suggesting that the mPTP was not opened.

CONCLUSIONS

Mitochondria have a precise role for determining cardioprotection or stunning in high-K+ cardioplegic rat hearts under I/R. Known protective drugs, such as Dzx and Ru360, which reduce the mitochondrial Ca2+-uptake, increased the stunning of CPG-rat hearts and reduced muscle economy, whereas 5-hydroxydecanoate and Clzp together increased the stunning by inducing mitochondrial Ca2+ overload.

Regulatory role of mitochondria in oxidative stress and atherosclerosis

Mitochondrial physiology and biogenesis play a crucial role in the initiation and progression of cardiovascular disease following oxidative stress-induced damage such as atherosclerosis (AST). Dysfunctional mitochondria caused by an increase in mitochondrial reactive oxygen species (ROS) production, accumulation of mitochondrial DNA damage, and respiratory chain deficiency induces death of endothelial/smooth muscle cells and favors plaque formation/rupture via the regulation of mitochondrial biogenesis-related genes such as peroxisome proliferator-activated receptor γ coactivator (PGC-1), although more detailed mechanisms still need further study. Based on the effect of healthy mitochondria produced by mitochondrial biogenesis on decreasing ROS-mediated cell death and the recent finding that the regulation of PGC-1 involves mitochondrial fusion-related protein (mitofusin), we thus infer the regulatory role of mitochondrial fusion/fission balance in AST pathophysiology. In this review, the first section discusses the possible association between AST-inducing factors and the molecular regulatory mechanisms of mitochondrial biogenesis and dynamics, and explains the role of mitochondria-dependent regulation in cell apoptosis during AST development. Furthermore, nitric oxide has the Janus-faced effect by protecting vascular damage caused by AST while being a reactive nitrogen species (RNS) which act together with ROS to damage cells. Therefore, in the second section we discuss mitochondrial ATP-sensitive K(+) channels, which regulate mitochondrial ion transport to maintain mitochondrial physiology, involved in the regulation of ROS/RNS production and their influence on AST/cardiovascular diseases (CVD). Through this review, we can further appreciate the multi-regulatory functions of the mitochondria involved in AST development. The understanding of these related mechanisms will benefit drug development in treating AST/CVD through targeted biofunctions of mitochondria.

Differential loss of cytochrome-c oxidase subunits in ischemia-reperfusion injury: exacerbation of COI subunit loss by PKC-epsilon inhibition

We have previously described a PKC-epsilon interaction with cytochrome oxidase subunit IV (COIV) that correlates with enhanced CO activity and cardiac ischemic preconditioning (PC). We therefore investigated the effects of PC and ischemia-reperfusion (I/R) injury on CO subunit levels in an anesthetized rat coronary ligation model. Homogenates prepared from the left ventricular regions at risk (RAR) and not at risk (RNAR) for I/R injury were fractionated into cell-soluble (S), 600 g low-speed centrifugation (L), gradient-purified mitochondrial (M), and 100,000 g particulate (P) fractions. In RAR tissue, PC (2 cycles of 5-min ischemia and 5-min reperfusion) decreased the COI in the P fraction ( approximately 29% of total cellular COI), suggesting changes in interfibrillar mitochondria. After 30 min of ischemia and 120 min of reperfusion, total COI levels decreased in the RAR by 72%. Subunit Va was also downregulated by 42% following prolonged I/R in the RAR. PC administered before I/R reduced the loss of COI in the M and P fractions approximately 30% and prevented COVa losses completely. We observed no losses in subunits Vb and VIIa following I/R alone; however, significant losses occurred when PC was administered before prolonged I/R. Delivery of a cell-permeable PKC-epsilon translocation inhibitor (epsilonV1-2) to isolated rat hearts before prolonged I/R dramatically increased COI loss, suggesting that PKC-epsilon protects COI levels. We propose that additional measures to protect CO subunits when coadministered with PC may improve its cardioprotection against I/R injury.

Myocardial ischemia tolerance in the newborn rat involving opioid receptors and mitochondrial K+ channels

Neonatal rat hearts are more tolerant to ischemia compared to adult rat hearts. We hypothesized that opioid receptors and mitochondrial potassium channels are involved in the elevated ischemia tolerance of neonatal rats. Newborn rats were treated by an intraperitoneal injection with sodium chloride (placebo, Pla; n = 7), naloxone (Nal; n = 8), or K+ (ATP) channel blocker 5-hydroxydecanoate (HD; n = 8), or were left untreated (sham; n = 8). Thirty minutes after injection, the rats were sacrificed and hearts were arrested cardioplegically and fixed with aldehyde fixative 90 min after global ischemia at room temperature. For control, newborn rat hearts were fixed immediately after sacrifice. Ventricular tissue blocks were prepared for electron microscopy. Mitochondrial (volume-weighted mean volume of mitochondria) and cardiomyocyte volume (cellular edema index, CEI) were estimated to quantify the ischemic injury. Compared to control myocardium, CEI was increased by 244% +/- 39% in sham, 173% +/- 28% in Nal, 142% +/- 25% in HD, and 101% +/- 24% in Pla (P < 0.05 between groups). Volume-weighted mean volume of mitochondria was increased by 514% +/- 235% in sham, 341% +/- 110% in Nal, 458% +/- 149% in HD, and 175% +/- 70% in Pla. Differences between Pla and other groups were significant (P < 0.01 for all). No significant difference was observed between the other groups. Thus, ischemic injury was smallest with placebo, indicating a mechanism similar to preconditioning induced by the intraperitoneal injection. This response was attenuated by blockade of opioid receptors and mitochondrial potassium channels, suggesting their involvement in the elevated ischemia tolerance of newborn rat hearts.

Reduction of myocardial infarct size by tetrahydrobiopterin: possible involvement of mitochondrial KATP channels activation through nitric oxide production

This study examined whether intravenous administration of tetrahydrobiopterin (BH4) reduces myocardial infarct size following ischemia/reperfusion (I/R) in rats, and the mechanisms of its protective effect were also investigated. Rats were subjected to 30 minutes of ischemia by ligation of the left coronary artery and 2 hours of reperfusion. The infarct size was determined as a percentage of the area at risk by triphenyltetrazolium staining. Intravenous administration of BH4 (0.01 mg/kg-1 mg/kg) significantly reduced the myocardial infarct size. Nitrite plus nitrate (NOx) and cGMP levels in the hearts were significantly increased by the treatment with BH4, and the infarct size-limiting effect of BH4 was abolished by the co-administration of NG-nitro-L-arginine methyl ester, a specific inhibitor of nitric oxide synthase, or 5-hydroxydecanoic acid, a specific inhibitor of mitochondrial ATP-sensitive potassium channel (mitoKATP channel). These findings suggest that BH4 has a cardioprotective effect against I/R in vivo, and its protective effect appeared to be involved in the opening of mitoKATP channels through increased nitric oxide production.