Bioenergetic consequences of opening the ATP-sensitive K(+) channel of heart mitochondria

Pharmacologic ROMK Inhibition Protects Against Myocardial Ischemia Reperfusion Injury

Mitochondrial ATP-sensitive K+ channels are closely linked to cardioprotection and are potential therapeutic targets during ischemia reperfusion (IR) injury. The renal outer medullary K+ channel isoform 2 (ROMK2) is an ATP-sensitive K+ channel found in the mitochondria of cardiomyocytes. While the germline knockout of ROMK does not mediate myocardial IR injury, the effect of ROMK loss of function on IR injury in the adult myocardium is unknown. By using a selective small molecule inhibitor of ROMK, we paradoxically found that mouse hearts were protected from IR injury after ROMK inhibition compared to vehicle-treated animals. In addition, we found that ROMK inhibition leads to exaggerated mitochondrial uncoupling and increased ROS production. Phosphatidylinositol 4,5-bisphosphate (PIP2), an activator of ROMK, increased the effect of ATP to hyperpolarize cardiac mitochondrial membrane potential. ROMK inhibition also increased mitochondrial swelling in the absence of ATP. In conclusion, pharmacologic ROMK inhibition protects the murine heart from IR injury and may promote a phenotype of enhanced mitochondrial matrix K+. ROMK may be more important during conditions that promote mitochondrial matrix K+ efflux than influx. Further research to understand its role in mitochondrial K+ handling and as a therapeutic target in IR injury is needed.

A glibenclamide analog lacking the cyclohexylurea portion fails to block ischemic preconditioning-induced mitochondrial and cardiac protection against ischemia/reperfusion injury

Despite significant research, there are no definitive therapies to prevent ischemia/reperfusion injury. During reperfusion, mitochondrial reactive oxygen species (ROS) cause cell damage. Ischemic preconditioning (IP), characterized by brief cycles of ischemia and reperfusion, activates mitochondrial ATP-sensitive potassium channels (mitoKATP) and provides cardioprotection. The aim of the present study is to investigate the impact of a truncated glibenclamide (lacking the cyclohexylurea portion - IMP-A) in ischemic preconditioning (IP)-mediated cardioprotection. Our study shows that IMP-A (2-5 μM) does not inhibit the protective effects of IP against ischemia/reperfusion damage in isolated rat hearts. In this context, IP hearts (with or without IMP-A) exhibited preserved cardiac function, as indicated by stable left ventricular developed pressure, maximal and minimal first derivatives, and rate-pressure product, along with a reduced infarct size following ischemia/reperfusion injury. Conversely, glibenclamide (2 μM - a well-characterized mitoKATP inhibitor) abolished the protective effects of IP against ischemia/reperfusion damage. Mitochondria isolated from reperfused IP hearts (treated or not with IMP-A) produced significantly lower levels of mitochondrial ROS and had lower susceptibility to Ca2+-induced swelling secondary to mitochondrial permeability transition pore (mPTP) opening. Additionally, IP hearts (treated or not with IMP-A) had preserved protein sulfhydryls. Glibenclamide elevated mitochondrial ROS production and negatively impacted mPTP and the sulfhydryl protection seen in IP hearts. Importantly, mitochondrial O2 consumption was preserved in IP hearts (treated or not with IMP-A), and this preservation was disrupted by glibenclamide but not by IMP-A. These findings suggest that the cyclohexylurea group of glibenclamide is essential for its ability to block IP-mediated cardioprotection, providing valuable insights for developing novel therapeutic strategies.

Dynamic Changes in Ion Channels during Myocardial Infarction and Therapeutic Challenges

In different areas of the heart, action potential waveforms differ due to differences in the expressions of sodium, calcium, and potassium channels. One of the characteristics of myocardial infarction (MI) is an imbalance in oxygen supply and demand, leading to ion imbalance. After MI, the regulation and expression levels of K+, Ca2+, and Na+ ion channels in cardiomyocytes are altered, which affects the regularity of cardiac rhythm and leads to myocardial injury. Myocardial fibroblasts are the main effector cells in the process of MI repair. The ion channels of myocardial fibroblasts play an important role in the process of MI. At the same time, a large number of ion channels are expressed in immune cells, which play an important role by regulating the in- and outflow of ions to complete intracellular signal transduction. Ion channels are widely distributed in a variety of cells and are attractive targets for drug development. This article reviews the changes in different ion channels after MI and the therapeutic drugs for these channels. We analyze the complex molecular mechanisms behind myocardial ion channel regulation and the challenges in ion channel drug therapy.

Activation of mitoKATP channels induces penile vasodilation and inhibits mitochondrial respiration and ROS production: Role of NO

OBJECTIVE

Mitochondrial ATP-sensitive K+ (mitoKATP) channels are involved in neuronal and cardiac protection from ischemia and oxidative stress. Penile erection is a neurovascular event mediated by relaxation of the erectile tissue via nitric oxide (NO) released from nerves and endothelium. In the present study, we investigated whether mitoKATP channels play a role in the control of penile vascular tone and mitochondrial dynamics, and the involvement of NO.

METHODS

The effect of the selective mitoKATP activator BMS191095 was examined on vascular tone, on mitochondrial bioenergetics by real-time measurements with Agilent Seahorse and on ROS production by MitoSOX fluorescence in freshly isolated microarteries.

RESULTS

BMS191095 and diazoxide relaxed penile arteries, BMS191095 being one order of magnitude more potent. BMS191095-induced relaxations were reduced by mechanical endothelium removal and by inhibitors of the nitric oxide synthase (NOS) and PI3K enzymes. The NO-dependent component of the relaxation to BMS191095 was impaired in penile arteries from insulin resistant obese rats. The blockers of mitoKATP channel 5-HD, sarcolemma KATP (sarcKATP) channel glibenclamide, and large conductance Ca2+-activated K+ (BKCa) channel iberiotoxin, inhibited relaxations to BMS191095 and to the NO donor SNAP. BMS191095 reduced the mitochondrial bioenergetic profile of penile arteries and attenuated mitochondrial ROS production. Blockade of endogenous NO impaired and exogenous NO mimicked, respectively, the inhibitory effects of BMS191095 on basal respiration and oxygen consumed for ATP synthesis. Exogenous NO exhibited dual inhibitory/stimulatory effects on mitochondrial respiration.

CONCLUSIONS

These results demonstrate that selective activation of mitoKATP channels causes penile vasodilation, attenuates ROS production and inhibits mitochondrial respiration in part by releasing endothelial NO. These mechanisms couple blood flow and metabolism in penile arterial wall and suggest that activation of vascular mitoKATP channels may protect erectile tissue against ischemic injury.

Role of mitochondrial potassium channels in ageing

Ageing is described as an inevitable decline in body functions over time and an increase in susceptibility to age-related diseases. Therefore, the increase of life expectancy is also viewed as a condition in which many elderly will develop age-related diseases and disabilities, such as cardiovascular, metabolic, neurological and oncological ones. Currently, several recognized cellular hallmarks of senescence are taken in consideration to evaluate the level of biological ageing and are the topic to plan preventive/curative anti-ageing interventions, including genomic instability, epigenetic alterations, and mitochondrial dysfunction. In this scenario, alterations in the function/expression of mitochondrial ion channels have been found in ageing and associated to an impairment of calcium cycling and a reduced mitochondrial membrane potential. Although several ion channels have been described at mitochondrial level, undoubtedly the mitochondrial potassium (mitoK) channels are the most investigated. Therefore, this review summarized the evidence that sheds to light a correlation between age-related diseases and alteration of mitoK channels, focusing the attention of the main age-related diseases, i.e. cardiovascular, neurological and oncological ones.

Diazoxide attenuates DOX-induced cardiotoxicity in cultured rat myocytes

Doxorubicin (DOX)-induced cardiotoxicity is a well known clinical problem, and many investigations have been made of its possible amelioration. We have investigated whether diazoxide (DIA), an agonist at mitochondrial ATP-sensitive potassium channels (mitoKATP), could reverse DOX-induced apoptotic myocardial cell loss, in cultured rat cardiomyocytes. The role of certain proteins in this pathway was also studied. The rat cardiomyocyte cell line (H9c2) was treated with DOX, and also co-treated with DOX and DIA, for 24 h. Distribution of actin filaments, mitochondrial membrane potential, superoxide dismutase (SOD) activity, total oxidant and antioxidant status (TOS and TAS, respectively), and some protein expressions, were assessed. DOX significantly decreased SOD activity, increased ERK1/2 protein levels, and depolarised the mitochondrial membrane, while DIA co-treatment inhibited such changes. DIA co-treatment ameliorated DOX-induced cytoskeletal changes via F-actin distribution and mitoKATP structure. Co-treatment also decreased ERK1/2 and cytochrome c protein levels. Cardiomyocyte loss due to oxidative stress-mediated apoptosis is a key event in DOX-induced cytotoxicity. DIA had protective effects on DOX-induced cardiotoxicity, via mitoKATP integrity, especially with elevated SUR2A levels; but also by a cascade including SOD/AMPK/ERK1/2. Therefore, DIA may be considered a candidate agent for protecting cardiomyocytes against DOX chemotherapy.

The mitochondrial ATP-dependent potassium channel (mitoKATP) controls skeletal muscle structure and function

MitoKATP is a channel of the inner mitochondrial membrane that controls mitochondrial K+ influx according to ATP availability. Recently, the genes encoding the pore-forming (MITOK) and the regulatory ATP-sensitive (MITOSUR) subunits of mitoKATP were identified, allowing the genetic manipulation of the channel. Here, we analyzed the role of mitoKATP in determining skeletal muscle structure and activity. Mitok-/- muscles were characterized by mitochondrial cristae remodeling and defective oxidative metabolism, with consequent impairment of exercise performance and altered response to damaging muscle contractions. On the other hand, constitutive mitochondrial K+ influx by MITOK overexpression in the skeletal muscle triggered overt mitochondrial dysfunction and energy default, increased protein polyubiquitination, aberrant autophagy flux, and induction of a stress response program. MITOK overexpressing muscles were therefore severely atrophic. Thus, the proper modulation of mitoKATP activity is required for the maintenance of skeletal muscle homeostasis and function.

KATP channels are regulators of programmed cell death and targets for the creation of novel drugs against ischemia/reperfusion cardiac injury

BACKGROUND

The use of percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a mortality rate of 5%-7%. It is clear that there is an urgent need to develop new drugs that can effectively prevent cardiac reperfusion injury. ATP-sensitive K+ (KATP ) channel openers (KCOs) can be classified as such drugs.

RESULTS

KCOs prevent irreversible ischemia and reperfusion injury of the heart. KATP channel opening promotes inhibition of apoptosis, necroptosis, pyroptosis, and stimulation of autophagy. KCOs prevent the development of cardiac adverse remodeling and improve cardiac contractility in reperfusion. KCOs exhibit antiarrhythmic properties and prevent the appearance of the no-reflow phenomenon in animals with coronary artery occlusion and reperfusion. Diabetes mellitus and a cholesterol-enriched diet abolish the cardioprotective effect of KCOs. Nicorandil, a KCO, attenuates major adverse cardiovascular event and the no-reflow phenomenon, reduces infarct size, and decreases the incidence of ventricular arrhythmias in patients with acute myocardial infarction.

CONCLUSION

The cardioprotective effect of KCOs is mediated by the opening of mitochondrial KATP (mitoKATP ) and sarcolemmal KATP (sarcKATP ) channels, triggered free radicals' production, and kinase activation.

Beneficial Effects of Halogenated Anesthetics in Cardiomyocytes: The Role of Mitochondria

In the last few years, the use of anesthetic drugs has been related to effects other than those initially related to their fundamental effect, hypnosis. Halogenated anesthetics, mainly sevoflurane, have been used as a therapeutic tool in patients undergoing cardiac surgery, thanks to the beneficial effect of the cardiac protection they generate. This effect has been described in several research studies. The mechanism by which they produce this effect has been associated with the effects generated by anesthetic preconditioning and postconditioning. The mechanisms by which these effects are induced are directly related to the modulation of oxidative stress and the cellular damage generated by the ischemia/reperfusion procedure through the overexpression of different enzymes, most of them included in the Reperfusion Injury Salvage Kinase (RISK) and the Survivor Activating Factor Enhancement (SAFE) pathways. Mitochondria is the final target of the different routes of pre- and post-anesthetic conditioning, and it is preserved from the damage generated in moments of lack of oxygen and after the recovery of the normal oxygen concentration. The final consequence of this effect has been related to better cardiac function in this type of patient, with less myocardial damage, less need for inotropic drugs to achieve normal myocardial function, and a shorter hospital stay in intensive care units. The mechanisms through which mitochondrial homeostasis is maintained and its relationship with the clinical effect are the basis of our review. From a translational perspective, we provide information regarding mitochondrial physiology and physiopathology in cardiac failure and the role of halogenated anesthetics in modulating oxidative stress and inducing myocardial conditioning.

δ-Opioid Receptor as a Molecular Target for Increasing Cardiac Resistance to Reperfusion in Drug Development

An analysis of published data and the results of our own studies reveal that the activation of a peripheral δ₂-opioid receptor (δ₂-OR) increases the cardiac tolerance to reperfusion. It has been found that this δ₂-OR is localized in cardiomyocytes. Endogenous opioids are not involved in the regulation of cardiac resistance to reperfusion. The infarct-limiting effect of the δ₂-OR agonist deltorphin II depends on the activation of several protein kinases, including PKCδ, ERK1/2, PI3K, and PKG. Hypothetical end-effectors of the cardioprotective effect of deltorphin II are the sarcolemmal K_ATP channels and the MPT pore.

Competitive interaction between ATP and GTP regulates mitochondrial ATP-sensitive potassium channels

Mitochondrial ATP-sensitive K⁺ channels (mitoKATP) have been recently characterized structurally, and possess a protein through which K⁺ enters mitochondria (MitoKIR), and a regulatory subunit (mitoSUR). The mitoSUR regulatory subunit is an ATP-binding cassette (ABC) protein isoform 8 (ABCB8). Opening these channels is known to be cardioprotective, but the molecular and physiological mechanisms that activate them are not fully known. Here, to better understand the molecular and physiological mechanisms of activators (GTP) and inhibitors (ATP) on the activity of mitoKATP, we exposed isolated mitochondria to both nucleotides. We also used molecular docking directed to the nucleotide-binding domain of human ABCB8/mitoSUR to test a comparative model of ATP and GTP effects. As expected, we find that ATP dose-dependently inhibits mitoKATP activity (IC₅₀ = 21.24 ± 1.4 mM). However, simultaneous exposure of mitochondria to GTP dose-dependently (EC₅₀ = 13.19 ± 1.33 mM) reversed ATP inhibition. Pharmacological and computational studies suggest that GTP reverses ATP activity competitively. Docking directed to the site of crystallized ADP reveals that both nucleotides bind to mitoSUR with high affinity, with their phosphates directed to the Mg²⁺ ion and the walker A motif of the protein (SGGGKTT). These effects, when combined, result in GTP binding, ATP displacement, mitochondrial ATP-sensitive K⁺ transport, and lower formation of reactive oxygen species. Overall, our findings demonstrate the basis for ATP and GTP binding in mitoSUR using a combination of biochemical, pharmacological, and computational experiments. Future studies may reveal the extent to which the balance between ATP and GTP actions contributes toward cardioprotection against ischemic events.

Regulation of Mitochondrial Permeability Transition Pore Opening by Monovalent Cations in Liver Mitochondria

The opening of the permeability transition pore (PTP) in mitochondria is a key event in the initiation of cell death in various pathologic states, including ischemia/reperfusion. The activation of K⁺ transport into mitochondria protects cells from ischemia/reperfusion. However, the role of K⁺ transport in PTP regulation is unclear. Here, we studied the role of K⁺ and other monovalent cations in the regulation of the PTP opening in an in vitro model. The registration of the PTP opening, membrane potential, Ca²⁺-retention capacity, matrix pH, and K⁺ transport was performed using standard spectral and electrode techniques. We found that the presence of all cations tested in the medium (K⁺, Na⁺, choline⁺, and Li⁺) strongly stimulated the PTP opening compared with sucrose. Several possible reasons for this were examined: the effect of ionic strength, the influx of cations through selective and non-selective channels and exchangers, the suppression of Ca²⁺/H⁺ exchange, and the influx of anions. The data obtained indicate that the mechanism of PTP stimulation by cations includes the suppression of K⁺/H⁺ exchange and acidification of the matrix, which facilitates the influx of phosphate. Thus, the K⁺/H⁺ exchanger and the phosphate carrier together with selective K⁺ channels compose a PTP regulatory triad, which might operate in vivo.

Diazoxide improves muscle function in association with improved dyslipidemia and decreased muscle oxidative stress in streptozotocin-induced diabetic rats

AIM/INTRODUCTION

Diabetes Mellitus is a chronic degenerative disease, and its main biochemical characteristic is hyperglycemia due to impaired insulin secretion, resistance to peripheral actions of insulin, or both. Hyperglycemia causes dyslipidemia and stimulates oxidative damage, leading to the main symptoms, such as fatigue and culminates in diabetic complications. Previous studies have shown that ATP-sensitive potassium channels counteract muscle fatigue and metabolic stress in healthy mouse models. To determine the effect of diazoxide on muscle strength development during diabetes, we tested the effect of diazoxide in streptozotocin-diabetic rats in muscle function, lipid profile and oxidative stress biomarkers.

MATERIALS AND METHODS

Wistar rats were divided into 4 groups of six animals each: (1) Control group, (2) diabetes group, (3) Control group + diazoxide, and (4) Diabetic + diazoxide (DB + DZX). 4 weeks after rats were sacrificed, soleus and extensor digitorum longus muscles (EDL) were extracted to prepare homogenates and serum was obtained for biochemical measurements. Oxidative damage was evaluated by the thiobarbituric acid method and the fluorescent for reactive oxygen species (ROS) probe 2,4-H2DCFDA, respectively.

RESULTS

Diabetic rats with diazoxide administration showed an increase in the development of muscle strength in both muscles; in turn, the onset of fatigue was longer compared to the group of diabetic rats without treatment. Regarding the lipid profile, diazoxide decreased total cholesterol levels in the group of diabetic rats treated with diazoxide (x̅46.2 mg/dL) compared to the untreated diabetic group (x̅=104.4 mg/dL); secondly, diazoxide decreased triglyceride concentrations (x̅=105.3 mg/dL) compared to the untreated diabetic rats (x̅=412.2 mg/dL) as well as the levels of very low-density lipoproteins (x̅=20.4 mg/dL vs. x̅=82.44 mg/dL). Regarding the various markers of oxidative stress, the diabetic group treated with diazoxide was able to reduce the concentrations of TBARS and total reactive oxygen species as well as preserve the concentrations of reduced glutathione.

CONCLUSION

Diazoxide administration in diabetic rats increases muscle strength development in EDL and soleus muscle, decreases fatigue, reduces cholesterol and triglyceride concentrations and improves oxidative stress parameters such as TBARS, ROS, and glutathione status.

Connexin 43 in Mitochondria: What Do We Really Know About Its Function?

Connexins are known for their ability to mediate cell-cell communication via gap junctions and also form hemichannels that pass ions and molecules over the plasma membrane when open. Connexins have also been detected within mitochondria, with mitochondrial connexin 43 (Cx43) being the best studied to date. In this review, we discuss evidence for Cx43 presence in mitochondria of cell lines, primary cells and organs and summarize data on its localization, import and phosphorylation status. We further highlight the influence of Cx43 on mitochondrial function in terms of respiration, opening of the mitochondrial permeability transition pore and formation of reactive oxygen species, and also address the presence of a truncated form of Cx43 termed Gja1-20k. Finally, the role of mitochondrial Cx43 in pathological conditions, particularly in the heart, is discussed.

The Regulation and Characterization of Mitochondrial-Derived Methylmalonic Acid in Mitochondrial Dysfunction and Oxidative Stress: From Basic Research to Clinical Practice

Methylmalonic acid (MMA) can act as a diagnosis of hereditary methylmalonic acidemia and assess the status of vitamin B12. Moreover, as a new potential biomarker, it has been widely reported to be associated with the progression and prognosis of chronic diseases such as cardiovascular events, renal insufficiency, cognitive impairment, and cancer. MMA accumulation may cause oxidative stress and impair mitochondrial function, disrupt cellular energy metabolism, and trigger cell death. This review primarily focuses on the mechanisms and epidemiology or progression in the clinical study on MMA.

The 40-Hz White Light-Emitting Diode (LED) Improves the Structure-Function of the Brain Mitochondrial KATP Channel and Respiratory Chain Activities in Amyloid Beta Toxicity

It has been described that using noninvasive exposure to 40-Hz white light LED reduces amyloid-beta, a peptide thought to initiate neurotoxic events in Alzheimer's disease (AD). However, the mechanisms remain to be identified. Since AD impairs mitochondrial potassium channels and respiratory chain activity, the objectives of the current study were to determine the effect of 40-Hz white light LED on structure-function of mitoK_ATP channel and brain mitochondrial respiratory chain activity, production of reactive oxygen species (ROS), and ΔΨ_m in AD. Single mitoK_ATP channel was considered using a channel incorporated into the bilayer lipid membrane and expression of mitoK_ATP-Kir6.1 subunit as a pore-forming subunit of the channel was determined using a western blot analysis in Aβ1-42 toxicity and light-treated rats. Our results indicated a severe decrease in mito-K_ATP channel permeation and Kir6.1 subunit expression coming from the Aβ1-42-induced neurotoxicity. Furthermore, we found that Aβ1-42-induced neurotoxicity decreased activities of complexes I and IV and increased ROS production and ΔΨ_m. Surprisingly, light therapy increased channel permeation and mitoK_ATP-Kir6.1 subunit expression. Noninvasive 40-Hz white light LED treatment also increased activities of complexes I and IV and decreased ROS production and ΔΨ_m up to ~ 70%. Here, we report that brain mito-K_ATP channel and respiratory chain are, at least in part, novel targets of 40-Hz white light LED therapy in AD.

ATP Synthase K+- and H+-fluxes Drive ATP Synthesis and Enable Mitochondrial K+-"Uniporter" Function: II. Ion and ATP Synthase Flux Regulation

We demonstrated that ATP synthase serves the functions of a primary mitochondrial K⁺ "uniporter," i.e., the primary way for K⁺ to enter mitochondria. This K⁺ entry is proportional to ATP synthesis, regulating matrix volume and energy supply-vs-demand matching. We show that ATP synthase can be upregulated by endogenous survival-related proteins via IF₁. We identified a conserved BH3-like domain of IF₁ which overlaps its "minimal inhibitory domain" that binds to the β-subunit of F₁. Bcl-xL and Mcl-1 possess a BH3-binding-groove that can engage IF₁ and exert effects, requiring this interaction, comparable to diazoxide to augment ATP synthase's H⁺ and K⁺ flux and ATP synthesis. Bcl-xL and Mcl-1, but not Bcl-2, serve as endogenous regulatory ligands of ATP synthase via interaction with IF₁ at this BH3-like domain, to increase its chemo-mechanical efficiency, enabling its function as the recruitable mitochondrial K_ATP-channel that can limit ischemia-reperfusion injury. Using Bayesian phylogenetic analysis to examine potential bacterial IF₁-progenitors, we found that IF₁ is likely an ancient (∼2 Gya) Bcl-family member that evolved from primordial bacteria resident in eukaryotes, corresponding to their putative emergence as symbiotic mitochondria, and functioning to prevent their parasitic ATP consumption inside the host cell.

Reversible and irreversible mitochondrial swelling: Effects of variable mitochondrial activity

An extended biophysical model was obtained by upgrading the previously reported one (Khmelinskii and Makarov, 2021). The upgraded model accommodates variations of solute transport rates through the inner mitochondrial membrane (IMM) within the mitochondrial population, described by a Gaussian distribution. However, the model may be used for any functional form of the distribution. The dynamics of system parameters as predicted by the current model differed from that predicted by the previous model in the same initial conditions (Khmelinskii and Makarov, 2021). The amount of change varied from one parameter to the other, remaining in the 1-38% range. The upgraded model fitted the available experimental data with a better accuracy (R = 0.993) compared to the previous model (R = 0.978) using the same experimental data (Khmelinskii and Makarov, 2021). The fitting procedure also estimated the Gaussian distribution parameters. The new model requires much larger computational resources, but given its higher accuracy, it may be used for better analysis of experimental data and for better prediction of MS dynamics in different initial conditions. Note that activities of individual mitochondria in mitochondrial populations should vary within biological tissues. Thus, the currently upgraded model is a better tool for biological and bio-medical applications. We believe that this model is much better adapted to the analysis of MS dynamics in vivo.

Supplementation of taurine improves ionic homeostasis and mitochondrial function in the rats exhibiting post-traumatic stress disorder-like symptoms

RATIONALE

Current pharmacotherapy for post-traumatic stress disorder (PTSD) is limited to few antidepressants. Mitochondrial dysfunction is observed in PTSD, along with altered potassium homeostasis. Nutritional supplementation of taurine can improve ionic homeostasis and thereby treat PTSD-like symptoms in rats.

AIM

The purpose is to study the pharmacological effect of taurine in stress re-stress-induced PTSD in rats.

METHODS

As per protocol, animals were restrained for 2 h then exposed to footshock (FS) (2 mA/10 s) followed by halothane-induced anesthesia. Behavioral assessments such as elevated plus maze (EPM) and Y-maze tests were performed on days 2, 8, and 32 of experimental protocol after re-stress. In addition, daily oral administration of taurine (100, 200, and 300 mg/kg) and paroxetine (PAX) (10 mg/kg) was done from D-8 to D-32 followed by re-stress. The plasma concentration of taurine, corticosterone, and potassium was measured on Day-32 along with mitochondrial function in discrete brain regions.

RESULTS

Sub-chronic administration of taurine in high and medium doses significantly ameliorated PTSD-like symptoms such as hyperarousal, anxiety, and improved spatial recognition memory. Taurine in all doses restored the plasma concentration of corticosterone and potassium. SRS-induced alterations in mitochondrial bioenergetics, complex enzyme activities, and reduced mitochondrial membrane potential in different brain regions were ameliorated by taurine.

CONCLUSION

Nutritional supplementation of taurine improves potassium ionic homeostasis, mitochondrial function, and attenuated PTSD-like symptoms in SRS subjected rats.

Pharmacological and molecular docking studies reveal that glibenclamide competitively inhibits diazoxide-induced mitochondrial ATP-sensitive potassium channel activation and pharmacological preconditioning

Mitochondrial ATP-sensitive potassium channels (mitoKATP) locate in the inner mitochondrial membrane and possess protective cellular properties. mitoKATP opening-induced cardioprotection (using the pharmacological agent diazoxide) is preventable by antagonists, such as glibenclamide. However, the mechanisms of action of these drugs and how mitoKATP respond to them are poorly understood. Here, we show data that reinforce the existence of a mitochondrial sulfonylurea receptor (mitoSUR) as part of the mitoKATP. We also show how diazoxide and glibenclamide compete for the same binding site in mitoSUR. A glibenclamide analog that lacks its cyclohexylurea portion (IMP-A) loses its ability to inhibit diazoxide-induced swelling. These results suggest that the cyclohexylureia portion of glibenclamide is indispensable for mitoKATP inhibition. Moreover, IMP-A did not suppress diazoxide-induced preconditioning (EC50 10.66 μM) in a rat model of a cardiac ischemia/reperfusion. Importantly, glibenclamide inhibited both diazoxide-induced cardioprotection (IC50 86 nM). We suggest that IMP-A must be used with caution since we found this drug possesses significant inhibitory effects on mitochondrial respiration. We characterized the binding of glibenclamide and diazoxide using a molecular simulation (docking) approach. Using the molecular structure of the ATP binding protein ABCB8 (pointed by others as the mitoSUR) we demonstrate that glibenclamide competitively inhibits diazoxide actions. This was reinforced (pharmacologically) in a competitive antagonism test. Taken together, these results bring valuable and novel insights into the pharmacological/biochemical aspects of mitokATP activation and cardioprotection. This study may lead to the discovery of novel therapeutic strategies that may impact ischemia-reperfusion injury.

Mitochondrial KATP channels stabilize intracellular Ca2+ during hypoxia in retinal horizontal cells of goldfish (Carassius auratus)

Neurons of the retina require oxygen to survive. In hypoxia, neuronal ATP production is impaired, ATP-dependent ion pumping is reduced, transmembrane ion gradients are dysregulated, and intracellular Ca2+ concentration ([Ca2+]i) increases enough to trigger excitotoxic cell death. Central neurons of the common goldfish (Carassius auratus) are hypoxia tolerant, but little is known about how goldfish retinas withstand hypoxia. To study the cellular mechanisms of hypoxia tolerance, we isolated retinal interneurons (horizontal cells; HCs), and measured [Ca2+]i with Fura-2. Goldfish HCs maintained [Ca2+]i throughout 1 h of hypoxia, whereas [Ca2+]i increased irreversibly in HCs of the hypoxia-sensitive rainbow trout (Oncorhynchus mykiss) with just 20 min of hypoxia. Our results suggest mitochondrial ATP-dependent K+ channels (mKATP) are necessary to stabilize [Ca2+]i throughout hypoxia. In goldfish HCs, [Ca2+]i increased when mKATP channels were blocked with glibenclamide or 5-hydroxydecanoic acid, whereas the mKATP channel agonist diazoxide prevented [Ca2+]i from increasing in hypoxia in trout HCs. We found that hypoxia protects against increases in [Ca2+]i in goldfish HCs via mKATP channels. Glycolytic inhibition with 2-deoxyglucose increased [Ca2+]i, which was rescued by hypoxia in a mKATP channel-dependent manner. We found no evidence of plasmalemmal KATP channels in patch-clamp experiments. Instead, we confirmed the involvement of KATP in mitochondria with TMRE imaging, as hypoxia rapidly (<5 min) depolarized mitochondria in a mKATP channel-sensitive manner. We conclude that mKATP channels initiate a neuroprotective pathway in goldfish HCs to maintain [Ca2+]i and avoid excitotoxicity in hypoxia. This model provides novel insight into the cellular mechanisms of hypoxia tolerance in the retina.

Reversible and irreversible mitochondrial swelling in vitro

Mitochondrial activity as regards ATP production strongly depends on mitochondrial swelling (MS) mode. Therefore, this work analyzes reversible and irreversible MS using a detailed biophysical model. The reported model includes mechanical properties of the inner mitochondrial membrane (IMM). The model describes MS dynamics for spherically symmetric, axisymmetric ellipsoidal and general ellipsoidal mitochondria. Mechanical stretching properties of the IMM were described by a second-rank rigidity tensor. The tensor components were estimated by fitting to the earlier reported results of in vitro experiments. The IMM rigidity constant of ca. 0.008 dyn/nm was obtained for linear deformations. The model also included membrane bending effects, which were small compared to those of membrane stretching. The model was also tested by simulation of the earlier reported experimental data and of the system dynamics at different initial conditions, predicting the system behavior. The transition criteria from reversible to irreversible swelling were determined and tested. The presently developed model is applicable directly to the analysis of in vitro experimental data, while additional improvements are necessary before it could be used to describe mitochondrial swelling in vivo. The reported theoretical model also provides an idea of physically consistent mechanism for the permeability transport pore (PTP) opening, which depends on the IMM stretching stress. In the current study, this idea is discussed briefly, but a detailed theoretical analysis of these ideas will be performed later. The currently developed model provides new understanding of the detailed MS mechanism and of the conditions for the transition between reversible and irreversible MS modes. On the other hand, the current model provides useful mathematical tools, that may be successfully used in mitochondrial biophysics research, and also in other applications, predicting the behavior of mitochondria in different conditions of the surrounding media in vitro or cellular cyto(sarco)plasm in vivo. These mathematical tools are based on real biophysical processes occurring in mitochondria. Thus, we note a significant progress in the theoretical approach, which may be used in real biological systems, compared to the earlier reported models. Significance of this study derives from inclusion of IMM mechanical properties, which directly impact the reversible and irreversible mitochondrial swelling dynamics. Reversible swelling corresponds to reversible IMM deformations, while irreversible swelling corresponds to irreversible deformations, with eventual membrane disruption. The IMM mechanical properties are directly dependent on the membrane biochemical composition and structure. The IMM deformationas are induced by osmotic pressure created by the ionic/neutral solute imbalance between the mitochondrial matrix media and the bulk solution in vitro, or cyto(sarco)plasm in vivo. The novelty of the reported model is in the biophysical mechanism detailing ionic and neutral solute transport for a large number of solutes, which were not taken into account in the earlier reported biophysical models of MS. Therefore, the reported model allows understanding response of mitochondria to the changes of initial concentration(s) of any of the solute(s) included in the model. Note that the values of all of the model parameters and kinetic constants have been estimated and the resulting complete model may be used for quantitative analysis of mitochondrial swelling dynamics in conditions of real in vitro experiments.

Targeting mitochondrial ion channels for cancer therapy

Pharmacological targeting of mitochondrial ion channels is emerging as a promising approach to eliminate cancer cells; as most of these channels are differentially expressed and/or regulated in cancer cells in comparison to healthy ones, this strategy may selectively eliminate the former. Perturbation of ion fluxes across the outer and inner membranes is linked to alterations of redox state, membrane potential and bioenergetic efficiency. This leads to indirect modulation of oxidative phosphorylation, which is/may be fundamental for both cancer and cancer stem cell survival. Furthermore, given the crucial contribution of mitochondria to intrinsic apoptosis, modulation of their ion channels leading to cytochrome c release may be of great advantage in case of resistance to drugs triggering apoptotic events upstream of the mitochondrial phase. In the present review, we give an overview of the known mitochondrial ion channels and of their modulators capable of killing cancer cells. In addition, we discuss state-of-the-art strategies using mitochondriotropic drugs or peptide-based approaches allowing a more efficient and selective targeting of mitochondrial ion channel-linked events.

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.

Mitochondrial K+ channels and their implications for disease mechanisms

The field of mitochondrial ion channels underwent a rapid development during the last decade, thanks to the molecular identification of some of the nuclear-encoded organelle channels and to advances in strategies allowing specific pharmacological targeting of these proteins. Thereby, genetic tools and specific drugs aided definition of the relevance of several mitochondrial channels both in physiological as well as pathological conditions. Unfortunately, in the case of mitochondrial K⁺ channels, efforts of genetic manipulation provided only limited results, due to their dual localization to mitochondria and to plasma membrane in most cases. Although the impact of mitochondrial K⁺ channels on human diseases is still far from being genuinely understood, pre-clinical data strongly argue for their substantial role in the context of several pathologies, including cardiovascular and neurodegenerative diseases as well as cancer. Importantly, these channels are druggable targets, and their in-depth investigation could thus pave the way to the development of innovative small molecules with huge therapeutic potential. In the present review we summarize the available experimental evidence that mechanistically link mitochondrial potassium channels to the above pathologies and underline the possibility of exploiting them for therapy.

Mechanism underlying sevoflurane-induced protection in cerebral ischemia–reperfusion injury

Cerebral ischemia is an extremely complex disease that can be caused by a variety of factors. Cerebral ischemia can cause great harm to human body. Sevoflurane is a volatile anesthetic that is frequently used in clinic, and has a lot of advantages, such as quick induction of general anesthesia, quick anesthesia recovery, no respiratory tract irritation, muscle relaxation, and small cycle effect. The mechanism of sevoflurane preconditioning or post-treatment induction is poorly understood. The purpose of this study was to illustrate the mechanism underlying sevoflurane-induced protection in cerebral ischemia–reperfusion injury and also provide theoretical guidance for future research.

Synthesis and cellular effects of a mitochondria-targeted inhibitor of the two-pore potassium channel TASK-3

The two-pore potassium channel TASK-3 has been shown to localize to both the plasma membrane and the mitochondrial inner membrane. TASK-3 is highly expressed in melanoma and breast cancer cells and has been proposed to promote tumor formation. Here we investigated whether pharmacological modulation of TASK-3, and specifically of mitochondrial TASK-3 (mitoTASK-3), had any effect on cancer cell survival and mitochondrial physiology. A novel, mitochondriotropic version of the specific TASK-3 inhibitor IN-THPP has been synthesized by addition of a positively charged triphenylphosphonium moiety. While IN-THPP was unable to induce apoptosis, mitoIN-THPP decreased survival of breast cancer cells and efficiently killed melanoma lines, which we show to express mitoTASK-3. Cell death was accompanied by mitochondrial membrane depolarization and fragmentation of the mitochondrial network, suggesting a role of the channel in the maintenance of the correct function of this organelle. In accordance, cells treated with mitoIN-THPP became rapidly depleted of mitochondrial ATP which resulted in activation of the AMP-dependent kinase AMPK. Importantly, cell survival was not affected in mouse embryonic fibroblasts and the effect of mitoIN-THPP was less pronounced in human melanoma cells stably knocked down for TASK-3 expression, indicating a certain degree of selectivity of the drug both for pathological cells and for the channel. In addition, mitoIN-THPP inhibited cancer cell migration to a higher extent than IN-THPP in two melanoma cell lines. In summary, our results point to the importance of mitoTASK-3 for melanoma cell survival and migration.

Mitochondrial Potassium Channels as Druggable Targets

Mitochondrial potassium channels have been described as important factors in cell pro-life and death phenomena. The activation of mitochondrial potassium channels, such as ATP-regulated or calcium-activated large conductance potassium channels, may have cytoprotective effects in cardiac or neuronal tissue. It has also been shown that inhibition of the mitochondrial Kv1.3 channel may lead to cancer cell death. Hence, in this paper, we examine the concept of the druggability of mitochondrial potassium channels. To what extent are mitochondrial potassium channels an important, novel, and promising drug target in various organs and tissues? The druggability of mitochondrial potassium channels will be discussed within the context of channel molecular identity, the specificity of potassium channel openers and inhibitors, and the unique regulatory properties of mitochondrial potassium channels. Future prospects of the druggability concept of mitochondrial potassium channels will be evaluated in this paper.

Nicorandil Affects Mitochondrial Respiratory Chain Function by Increasing Complex III Activity and ROS Production in Skeletal Muscle Mitochondria

Adenosine triphosphate (ATP)-dependent potassium channels openers (K_ATP) protect skeletal muscle against function impairment through the activation of the mitochondrial K_ATP channels (mitoK_ATP). Previous reports suggest that modulators of the mitochondrial K_ATP channels have additional effects on isolated mitochondria. To determine whether the K_ATP channel opener nicorandil has non-specific effects that explain its protective effect through the mitochondrial function, chicken muscle mitochondria were isolated, and respiration rate was determined pollarographically. The activity of the electron transport chain (ETC) complexes (I-IV) was measured using a spectrophotometric method. Reactive oxygen species (ROS) levels and lipid peroxidation were assessed using flow cytometry and thiobarbituric acid assay, respectively. Both K_ATP channel opener nicorandil and K_ATP channel blocker 5-hydroxydecanoate (5-HD) decreased mitochondrial respiration; nicorandil increased complex III activity and decreased complex IV activity. The effects of nicorandil on complex III were antagonized by 5-HD. Nicorandil increased ROS levels, effect reverted by either 5-HD or the antioxidant N-2-mercaptopropionyl glycine (MPG). None of these drugs affected lipid peroxidation levels. These findings suggest that K_ATP channel opener nicorandil increases mitochondrial ROS production from complex III. This results by partially blocking electron flow in the complex IV, setting electron carriers in a more reduced state, which is favored by the increase in complex III activity by nicorandil. Overall, our study showed that nicorandil like other mitochondrial K_ATP channel openers might not act through mitoK_ATP channel activation.

Signaling pathways targeting mitochondrial potassium channels

In this review, we describe key signaling pathways regulating potassium channels present in the inner mitochondrial membrane. The signaling cascades covered here include phosphorylation, redox reactions, modulation by calcium ions and nucleotides. The following types of potassium channels have been identified in the inner mitochondrial membrane of various tissues: ATP-sensitive, Ca²⁺-activated, voltage-gated and two-pore domain potassium channels. The direct roles of these channels involve regulation of mitochondrial respiration, membrane potential and synthesis of reactive oxygen species (ROS). Changes in channel activity lead to diverse pro-life and pro-death responses in different cell types. Hence, characterizing the signaling pathways regulating mitochondrial potassium channels will facilitate understanding the physiological role of these proteins. Additionally, we describe in this paper certain regulatory mechanisms, which are unique to mitochondrial potassium channels.

Diazoxide affects mitochondrial bioenergetics by the opening of mKATP channel on submicromolar scale

Background

Cytoprotection afforded by mitochondrial ATP-sensitive K⁺-channel (mK_ATP-channel) opener diazoxide (DZ) largely depends on the activation of potassium cycle with eventual modulation of mitochondrial functions and ROS production. However, generally these effects were studied in the presence of Mg∙ATP known to block K⁺ transport. Thus, the purpose of our work was the estimation of DZ effects on K⁺ transport, K⁺ cycle and ROS production in rat liver mitochondria in the absence of Mg∙ATP.

Results

Without Mg·ATP, full activation of native mK_ATP-channel, accompanied by the increase in ATP-insensitive K⁺ uptake, activation of K⁺-cycle and respiratory uncoupling, was reached at ≤0.5 μM of DZ,. Higher diazoxide concentrations augmented ATP-insensitive K⁺ uptake, but not mK_ATP-channel activity. mK_ATP-channel was blocked by Mg·ATP, reactivated by DZ, and repeatedly blocked by mK_ATP-channel blockers glibenclamide and 5-hydroxydecanoate, whereas ATP-insensitive potassium transport was blocked by Mg²⁺ and was not restored by DZ. High sensitivity of potassium transport to DZ in native mitochondria resulted in suppression of mitochondrial ROS production caused by the activation of K⁺-cycle on sub-micromolar scale. Based on the oxygen consumption study, the share of mK_ATP-channel in respiratory uncoupling by DZ was found.

Conclusions

The study of mK_ATP-channel activation by diazoxide in the absence of MgATP discloses novel, not described earlier, aspects of mK_ATP-channel interaction with this drug. High sensitivity of mK_ATP-channel to DZ results in the modulation of mitochondrial functions and ROS production by DZ on sub-micromolar concentration scale. Our experiments led us to the hypothesis that under the conditions marked by ATP deficiency affinity of mK_ATP-channel to DZ can increase, which might contribute to the high effectiveness of this drug in cardio- and neuroprotection.

Global knockout of ROMK potassium channel worsens cardiac ischemia-reperfusion injury but cardiomyocyte-specific knockout does not: Implications for the identity of mitoKATP

The renal-outer-medullary‑potassium (ROMK) channel, mutated in Bartter's syndrome, regulates ion exchange in kidney, but its extra-renal functions remain unknown. Additionally, ROMK was postulated to be the pore-forming subunit of the mitochondrial ATP-sensitive K+ channel (mitoKATP), a mediator of cardioprotection. Using global and cardiomyocyte-specific knockout mice (ROMK-GKO and ROMK-CKO respectively), we characterize the effects of ROMK knockout on mitochondrial ion handling, the response to pharmacological KATP channel modulators, and ischemia/reperfusion (I/R) injury. Mitochondria from ROMK-GKO hearts exhibited a lower threshold for Ca2+-triggered permeability transition pore (mPTP) opening but normal matrix volume changes during oxidative phosphorylation. Isolated perfused ROMK-GKO hearts exhibited impaired functional recovery and increased infarct size when I/R was preceded by an ischemic preconditioning (IPC) protocol. Because ROMK-GKO mice exhibited severe renal defects and cardiac remodeling, we further characterized ROMK-CKO hearts to avoid confounding systemic effects. Mitochondria from ROMK-CKO hearts had unchanged matrix volume responses during oxidative phosphorylation and still swelled upon addition of a mitoKATP opener, but exhibited a lower threshold for mPTP opening, similar to GKO mitochondria. Nevertheless, I/R induced damage was not exacerbated in ROMK-CKO hearts, either ex vivo or in vivo. Lastly, we examined the response of ROMK-CKO hearts to ex vivo I/R injury with or without IPC and found that IPC still protected these hearts, suggesting that cardiomyocyte ROMK does not participate significantly in the cardioprotective pathway elicited by IPC. Collectively, our findings from these novel strains of mice suggest that cardiomyocyte ROMK is not a central mediator of mitoKATP function, although it can affect mPTP activation threshold.

Effects of Pinacidil and Calcium on Succinate-Energized Rat Heart Mitochondria in the Presence of Rotenone

The effect of pinacidil was studied on calcium-loaded rat heart mitochondria (RHM) in the presence of succinate and rotenone. In experiments with pinacidil, the swelling of these mitochondria increased in media with NH₄NO₃ or K-acetate, but the inner membrane potential (ΔΨ_mito) and the respiration in 3 or 2,4-dinitrophenol-stimulated states of these organelles decreased due to the opening of the mitochondrial permeability transition pore (MPTP) in their inner membrane. These effects were inhibited by cyclosporin A and ADP. It was concluded that the protective effect of pinacidil in the cardiac muscle under ischemia/reperfusion may be associated with both the stimulation of mitochondrial swelling and a decrease in RHM calcium overload resulted in ΔΨ_mito fall due to mild uncoupling effect of pinacidil.

Mitochondrial dynamics, a key executioner in neurodegenerative diseases

Neurodegenerative diseases (NDs) are the group of disorder that includes brain, peripheral nerves, spinal cord and results in sensory and motor neuron dysfunction. Several studies have shown that mitochondrial dynamics and their axonal transport play a central role in most common NDs such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and Amyotrophic Lateral Sclerosis (ALS) etc. In normal physiological condition, there is a balance between mitochondrial fission and fusion process while any alteration to these processes cause defect in ATP (Adenosine Triphosphate) biogenesis that lead to the onset of several NDs. Also, mitochondria mediated ROS may induce lipid and protein peroxidation, energy deficiency environment in the neurons and results in cell death and defective neurotransmission. Though, mitochondria is a well-studied cell organelle regulating the cellular energy demands but still, its detail role or association in NDs is under observation. In this review, we have summarized an updated mitochondria and their possible role in different NDs with the therapeutic strategy to improve the mitochondrial functions.

The slow force response to stretch: Controversy and contradictions

When exposed to an abrupt stretch, cardiac muscle exhibits biphasic active force enhancement. The initial, instantaneous, force enhancement is well explained by the Frank-Starling mechanism. However, the cellular mechanisms associated with the second, slower phase remain contentious. This review explores hypotheses regarding this "slow force response" with the intention of clarifying some apparent contradictions in the literature. The review is partitioned into three sections. The first section considers pathways that modify the intracellular calcium handling to address the role of the sarcoplasmic reticulum in the mechanism underlying the slow force response. The second section focuses on extracellular calcium fluxes and explores the identity and contribution of the stretch-activated, non-specific, cation channels as well as signalling cascades associated with G-protein coupled receptors. The final section introduces promising candidates for the mechanosensor(s) responsible for detecting the stretch perturbation.

Use the Protonmotive Force: Mitochondrial Uncoupling and Reactive Oxygen Species

Mitochondrial respiration results in an electrochemical proton gradient, or protonmotive force (pmf), across the mitochondrial inner membrane. The pmf is a form of potential energy consisting of charge (∆ψ_m) and chemical (∆pH) components, that together drive ATP production. In a process called uncoupling, proton leak into the mitochondrial matrix independent of ATP production dissipates the pmf and energy is lost as heat. Other events can directly dissipate the pmf independent of ATP production as well, such as chemical exposure or mechanisms involving regulated mitochondrial membrane electrolyte transport. Uncoupling has defined roles in metabolic plasticity and can be linked through signal transduction to physiologic events. In the latter case, the pmf impacts mitochondrial reactive oxygen species (ROS) production. Although capable of molecular damage, ROS also have signaling properties that depend on the timing, location, and quantity of their production. In this review, we provide a general overview of mitochondrial ROS production, mechanisms of uncoupling, and how these work in tandem to affect physiology and pathologies, including obesity, cardiovascular disease, and immunity. Overall, we highlight that isolated bioenergetic models-mitochondria and cells-only partially recapitulate the complex link between the pmf and ROS signaling that occurs in vivo.

Romo1 is a mitochondrial nonselective cation channel with viroporin-like characteristics

Romo1 regulates mitochondrial reactive oxygen species production and acts as an essential redox sensor in mitochondrial dynamics. Lee et al. demonstrate that Romo1 is a unique mitochondrial ion channel with viroporin-like characteristics that distinguish Romo1 from other known eukaryotic ion channels.

Reactive oxygen species (ROS) modulator 1 (Romo1) is a nuclear-encoded mitochondrial inner membrane protein known to regulate mitochondrial ROS production and to act as an essential redox sensor in mitochondrial dynamics. Although its physiological roles have been studied for a decade, the biophysical mechanisms that explain these activities of Romo1 are unclear. In this study, we report that Romo1 is a unique mitochondrial ion channel that differs from currently identified eukaryotic ion channels. Romo1 is a highly conserved protein with structural features of class II viroporins, which are virus-encoded nonselective cation channels. Indeed, Romo1 forms a nonselective cation channel with its amphipathic helical transmembrane domain necessary for pore-forming activity. Notably, channel activity was specifically inhibited by Fe²⁺ ions, an essential transition metal ion in ROS metabolism. Using structural bioinformatics, we designed an experimental data–guided structural model of Romo1 with a rational hexameric structure. We propose that Romo1 establishes a new category of viroporin-like nonselective cation channel in eukaryotes.

Evidence for a mitochondrial ATP-regulated potassium channel in human dermal fibroblasts

Mitochondrial ATP-regulated potassium channels are present in the inner membrane of the mitochondria of various cells. In the present study, we show for the first time mitochondrial ATP-regulated potassium channels in human dermal fibroblast cells. Using the patch-clamp technique on the inner mitochondrial membrane of fibroblasts, we detected a potassium channel with a mean conductance equal to 100 pS in symmetric 150 mM KCl. The activity of this channel was inhibited by a complex of ATP/Mg²⁺ and activated by potassium channel openers such as diazoxide or BMS 191095. Channel activity was inhibited by antidiabetic sulfonylurea glibenclamide and 5-hydroxydecanoic acid. The influence of substances modulating ATP-regulated potassium channel activity on oxygen consumption and membrane potential of isolated fibroblast mitochondria was also studied. Additionally, the potassium channel opener diazoxide lowered the amount of superoxide formed in isolated fibroblast mitochondria. Using reverse transcriptase-PCR, we found an mRNA transcript for the KCNJ1(ROMK) channel. The presence of ROMK protein was observed in the inner mitochondrial membrane fraction. Moreover, colocalization of the ROMK protein and a mitochondrial marker in the mitochondria of fibroblast cells was shown by immunofluorescence. In summary, the ATP-regulated mitochondrial potassium channel in a dermal fibroblast cell line have been identified.

Endogenous and Agonist-induced Opening of Mitochondrial Big Versus Small Ca2+-sensitive K+ Channels on Cardiac Cell and Mitochondrial Protection

Both big (BKCa) and small (SKCa) conductance Ca-sensitive K channels are present in mammalian cardiac cell mitochondria (m). We used pharmacological agonists and antagonists of BKCa and SKCa channels to examine the importance of endogenous opening of these channels and the relative contribution of either or both of these channels to protect against contractile dysfunction and reduce infarct size after ischemia reperfusion (IR) injury through a mitochondrial protective mechanism. After global cardiac IR injury of ex vivo perfused Guinea pig hearts, we found the following: both agonists NS1619 (for BKCa) and DCEB (for SKCa) improved contractility; BKCa antagonist paxilline (PAX) alone or with SKCa antagonist NS8593 worsened contractility and enhanced infarct size; both antagonists PAX and NS8593 obliterated protection by their respective agonists; BKCa and SKCa antagonists did not block protection afforded by SKCa and BKCa agonists, respectively; and all protective effects by the agonists were blocked by scavenging superoxide anions (O2) with Mn(III) tetrakis (4-benzoic acid) porphyrin (TBAP). Contractile function was inversely associated with global infarct size. In in vivo rats, infusion of NS8593, PAX, or both antagonists enhanced regional infarct size while infusion of either NS1619 or DCEB reduced infarct size. In cardiac mitochondria isolated from ex vivo hearts after IR, combined SKCa and BKCa agonists improved respiratory control index and Ca retention capacity compared with IR alone, whereas the combined antagonists did not alter respiratory control index but worsened Ca retention capacity. Although the differential protective bioenergetics effects of endogenous or exogenous BKCa and SKCa channel opening remain unclear, each channel likely responds to different sensing Ca concentrations and voltage gradients over time during oxidative stress-induced injury to individually or together protect cardiac mitochondria and myocytes.

A Protective Role of Glibenclamide in Inflammation-Associated Injury

Glibenclamide is the most widely used sulfonylurea drug for the treatment of type 2 diabetes mellitus (DM). Recent studies have suggested that glibenclamide reduced adverse neuroinflammation and improved behavioral outcomes following central nervous system (CNS) injury. We reviewed glibenclamide's anti-inflammatory effects: abundant evidences have shown that glibenclamide exerted an anti-inflammatory effect in respiratory, digestive, urological, cardiological, and CNS diseases, as well as in ischemia-reperfusion injury. Glibenclamide might block K_ATP channel, Sur1-Trpm4 channel, and NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome activation, decrease the production of proinflammatory mediators (TNF-α, IL-1β, and reactive oxygen species), and suppress the accumulation of inflammatory cells. Glibenclamide's anti-inflammation warrants further investigation.

The Slo(w) path to identifying the mitochondrial channels responsible for ischemic protection

Mitochondria play an important role in tissue ischemia and reperfusion (IR) injury, with energetic failure and the opening of the mitochondrial permeability transition pore being the major causes of IR-induced cell death. Thus, mitochondria are an appropriate focus for strategies to protect against IR injury. Two widely studied paradigms of IR protection, particularly in the field of cardiac IR, are ischemic preconditioning (IPC) and volatile anesthetic preconditioning (APC). While the molecular mechanisms recruited by these protective paradigms are not fully elucidated, a commonality is the involvement of mitochondrial K⁺ channel opening. In the case of IPC, research has focused on a mitochondrial ATP-sensitive K⁺ channel (mitoK_ATP), but, despite recent progress, the molecular identity of this channel remains a subject of contention. In the case of APC, early research suggested the existence of a mitochondrial large-conductance K⁺ (BK, big conductance of potassium) channel encoded by the Kcnma1 gene, although more recent work has shown that the channel that underlies APC is in fact encoded by Kcnt2 In this review, we discuss both the pharmacologic and genetic evidence for the existence and identity of mitochondrial K⁺ channels, and the role of these channels both in IR protection and in regulating normal mitochondrial function.

Stimulation of mitochondrial ATP synthase activity - a new diazoxide-mediated mechanism of cardioprotection

Pharmacological preconditioning by diazoxide and a model of experimental streptozotocin-induced acute diabetes mellitus (STZ-DM) provided similar levels of cardioprotection assessed as limiting myocardial infarct size. The aim was to explore the possibility of existence of another in vitro mechanism, which could be contributory to cardioprotection mediated by diazoxide treatment. Mitochondrial membrane fluidity and ATP synthase activity in isolated heart mitochondria were determined under the influence of two factors, STZ-DM condition and treatment with diazoxide. Both factors independently increased the ATP synthase activity (p<0.05), as no interaction effect was observed upon the combination of STZ-DM with diazoxide. On the other hand, the mitochondrial membrane fluidity was significantly increased by STZ-DM only; no significant main effect for diazoxide was found. Based on the results from measurements of enzyme kinetics, we assume a direct interaction of diazoxide with the molecule of ATP synthase stimulated its activity by noncompetitive activation. Our present work revealed, for the first time, that cardioprotection induced by diazoxide may not be caused exclusively by mitochondrial K(ATP) opening, but presumably also by a direct interaction of diazoxide with ATP synthase, although the mechanisms for achieving this activation cannot be fully delineated.

Sevoflurane postconditioning protects the myocardium against ischemia/reperfusion injury via activation of the JAK2-STAT3 pathway

BACKGROUND

Sevoflurane postconditioning (S-post) has similar cardioprotective effects as ischemic preconditioning. However, the underlying mechanism of S-post has not been fully elucidated. Janus kinase signaling transduction/transcription activator (JAK2-STAT3) plays an important role in cardioprotection. The purpose of this study was to determine whether the cardioprotective effects of S-post are associated with activation of the JAK2-STAT3 signal pathway.

METHODS

An adult male Sprague-Dawley (SD) rat model of myocardial ischemia/reperfusion (I/R) injury was established using the Langendorff isolated heart perfusion apparatus. At the beginning of reperfusion, 2.4% sevoflurane alone or in combination with AG490 (a JAK2 selective inhibitor) was used as a postconditioning treatment. The cardiac function indicators, myocardial infarct size, lactic dehydrogenase (LDH) release, mitochondrial ultrastructure, mitochondrial reactive oxygen species (ROS) generation rates, ATP content, protein expression of p-JAK, p-STAT3, Bcl-2 and Bax were measured.

RESULTS

Compared with the I/R group, S-post significantly increased the expression of p-JAK, p-STAT3 and Bcl-2 and reduced the protein expression of Bax, which markedly decreased the myocardial infarction areas, improved the cardiac function indicators and the mitochondrial ultrastructure, decreased the mitochondrial ROS and increased the ATP content. However, the cardioprotective effects of S-post were abolished by treatment with a JAK2 selective inhibitor (p < 0.05).

CONCLUSION

This study demonstrates that the cardioprotective effects of S-post are associated with the activation of JAK2-STAT3. The mechanism may be related to an increased expression of p-JAK2 and p-STAT3 after S-post, which reduced mitochondrial ROS generation and increased mitochondrial ATP content, thereby reducing apoptosis and myocardial infarct size.

[Vasopressors and inotropes: use in paediatrics]

The cardiovascular system is a dynamic system, which is required to ensure adequate delivery of oxygen, nutrients, and hormones to the tissues that are necessary for cell metabolism. It also synthesises and modifies the vasoactive components that regulate vascular tone and myocardial function. These vasoactive components have demonstrated their beneficial effects in the management of paediatric patients in a critical condition with heart failure and shock. However, their use and abuse brings harmful effects, increases mortality, and is associated with arrhythmias. An increase in myocardial oxygen consumption favours the presence of ischaemia, therefore it is necessary to know the mechanism of action and indications of these drugs to minimise their harmful effects. The purpose of this review is to describe the pharmacology and clinical applications of inotropic and vasopressor agents in the paediatric patient in acritical condition.

Cardioprotection with halogenated gases: how does it occur?

Numerous studies have studied the effect of halogenated agents on the myocardium, highlighting the beneficial cardiac effect of the pharmacological mechanism (preconditioning and postconditioning) when employed before and after ischemia in patients with ischemic heart disease. Anesthetic preconditioning is related to the dose-dependent signal, while the degree of protection is related to the concentration of the administered drug and the duration of the administration itself. Triggers for postconditioning and preconditioning might have numerous pathways in common; mitochondrial protection and a decrease in inflammatory mediators could be the major biochemical elements. Several pathways have been identified, including attenuation of NFκB activation and reduced expression of TNFα, IL-1, intracellular adhesion molecules, eNOS, the hypercontraction reduction that follows reperfusion, and antiapoptotic activating kinases (Akt, ERK1/2). It appears that the preconditioning and postconditioning triggers have numerous similar paths. The key biochemical elements are protection of the mitochondria and reduction in inflammatory mediators, both of which are developed in various ways. We have studied this issue, and have published several articles on cardioprotection with halogenated gases. Our results confirm greater cardioprotection through myocardial preconditioning in patients anesthetized with sevoflurane compared with propofol, with decreasing levels of troponin and N-terminal brain natriuretic peptide prohormone. The difference between our studies and previous studies lies in the use of sedation with sevoflurane in the postoperative period. The results could be related to a prolonged effect, in addition to preconditioning and postconditioning, which could enhance the cardioprotective effect of sevoflurane in the postoperative period. With this review, we aim to clarify the importance of various mechanisms involved in preconditioning and postconditioning with halogenated gases, as supported by our studies.

Therapeutic effects of oral liothyronine on aluminum phosphide poisoning as an adjuvant therapy

Background:

In aluminum phosphide (AlP) poisoning, death is mainly due to cardiovascular failure and refractory acute heart failure. There is a lot of evidence showing thyroid hormones have cardioprotective effects.

Objective:

The purpose of this study was to evaluate the effect of oral liothyronine in the treatment of AlP poisoning.

Methods:

Twenty-four patients from intensive care unit of Baharloo Hospital, Tehran, Iran, were included based on the inclusion and exclusion criteria. They were randomly divided into two parallel groups of 12 cases and 12 controls. Intervention in the case group was administration of 50 µg liothyronine via nasogastric tube after gastric lavage, in the first 6 h of poisoning. In both groups, the routine treatment of AlP poisoning was performed. Blood samples were prepared at the beginning of the study and after 12 h. Patients were followed up till discharge from the hospital or death.

Results:

The findings demonstrated that oral liothyronine was able to significantly improve systolic blood pressure, arterial blood pH, and total thiol molecules and also could decrease lipid peroxidation, increase catalase activity, and prevent further decline in total antioxidant capacity.

Conclusion:

Liothyronine administration is effective in controlling AlP poisoning and can improve patients’ outcome.

Bioenergetic and volume regulatory effects of mitoKATP channel modulators protect against hypoxia-reoxygenation-induced mitochondrial dysfunction

The mitochondrial ATP-sensitive K(+) (mitoKATP) channel plays a significant role in mitochondrial physiology and protects against ischemic reperfusion injury in mammals. Although fish frequently face oxygen fluctuations in their environment, the role of the mitoKATP channel in regulating the responses to oxygen stress is rarely investigated in this class of animals. To elucidate whether and how the mitoKATP channel protects against hypoxia-reoxygenation (H-R)-induced mitochondrial dysfunction in fish, we first determined the mitochondrial bioenergetic effects of two key modulators of the channel, diazoxide and 5-hydroxydecanoate (5-HD), using a wide range of doses. Subsequently, the effects of low and high doses of the modulators on mitochondrial bioenergetics and volume under normoxia and after H-R using buffers with and without magnesium and ATP (Mg-ATP) were tested. In the absence of Mg-ATP (mitoKATP channel open), both low and high doses of diazoxide improved mitochondrial coupling, but only the high dose of 5-HD reversed the post-H-R coupling-enhancing effect of diazoxide. In the presence of Mg-ATP (mitoKATP channel closed), diazoxide at the low dose improved coupling post-H-R, and this effect was abolished by 5-HD at the low dose. Interestingly, both low and high doses of diazoxide reversed H-R-induced swelling under mitoKATP channel open conditions, but this effect was not sensitive to 5-HD. Under mitoKATP channel closed conditions, diazoxide at the low dose protected the mitochondria from H-R-induced swelling and 5-HD at the low dose reversed this effect. In contrast, diazoxide at the high dose failed to reduce the swelling caused by H-R, and the addition of the high dose of 5-HD enhanced mitochondrial swelling. Overall, our study showed that in the presence of Mg-ATP, both opening of mitoKATP channels and bioenergetic effects of diazoxide were protective against H-R in fish mitochondria, while in the absence of Mg-ATP only the bioenergetic effect of diazoxide was protective.