Sarcolemmal KATP Channels Research Articles

Angiotensin 1-7 increases cardiac tolerance to ischemia/reperfusion and mitigates adverse remodeling of the heart-The signaling mechanism.

The high mortality rate of patients with acute myocardial infarction (AMI) remains the most pressing issue of modern cardiology. Over the past 10years, there has been no significant reduction in mortality among patients with AMI. It is quite obvious that there is an urgent need to develop fundamentally new drugs for the treatment of AMI. Angiotensin 1-7 has some promise in this regard. The objective of this article is analysis of published data on the cardioprotective properties of angiotensin 1-7. PubMed, Scopus, Science Direct, and Google Scholar were used to search articles for this study. Angiotensin 1-7 increases cardiac tolerance to ischemia/reperfusion and mitigates adverse remodeling of the heart. Angiotensin 1-7 can prevent not only ischemic but also reperfusion cardiac injury. The activation of the Mas receptor plays a key role in these effects of angiotensin 1-7. Angiotensin 1-7 alleviates Ca2+ overload of cardiomyocytes and reactive oxygen species production in ischemia/reperfusion (I/R) of the myocardium. It is possible that both effects are involved in angiotensin 1-7-triggered cardiac tolerance to I/R. Furthermore, angiotensin 1-7 inhibits apoptosis of cardiomyocytes and stimulates autophagy of cells. There is also indirect evidence suggesting that angiotensin 1-7 inhibits ferroptosis in cardiomyocytes. Moreover, angiotensin 1-7 possesses anti-inflammatory properties, possibly achieved through NF-kB activity inhibition. Phosphoinositide 3-kinase, Akt, and NO synthase are involved in the infarct-reducing effect of angiotensin 1-7. However, the specific end-effector of the cardioprotective impact of angiotensin 1-7 remains unknown. The molecular nature of the end-effector of the infarct-limiting effect of angiotensin 1-7 has not been elucidated. Perhaps, this end-effector is the sarcolemmal KATP channel or the mitochondrial KATP channel.

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 KATP channels and the MPT pore.

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

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. 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. 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.

Attenuation of ST-segment elevation by ischemic preconditioning: Reflection of cardioprotection in Göttingen but not in Ossabaw minipigs

BackgroundIschemic preconditioning (IPC; brief cycles of coronary occlusion/ reperfusion) reduces myocardial infarct size. The ST-segment elevation during coronary occlusion is progressively attenuated with increasing number of IPC cycles. Progressive attenuation of ST-segment elevation is considered a result of sarcolemmal KATP channel activation and has been considered to reflect and predict IPC's cardioprotection. We have recently demonstrated that IPC failed to reduce infarct size in minipigs of a particular strain (Ossabaw), which had a genetic predisposition to develop, but not yet established a metabolic syndrome. To determine whether or not Ossabaw minipigs nevertheless had attenuated ST-segment elevation over repetitive IPC cycles, we compared Göttingen vs. Ossabaw minipigs in which IPC reduces infarct size. Methods and resultsWe analyzed surface chest electrocardiographic (ECG) recordings of anesthetized open-chest contemporary Göttingen (n = 43) and Ossabaw minipigs (n = 53). Both minipig strains were subjected to 60 min coronary occlusion and 180 min reperfusion without or with IPC (3 × 5 min/ 10 min coronary occlusion/ reperfusion). ST-segment elevations during the repetitive coronary occlusions were analyzed. In both minipig strains, IPC attenuated ST-segment elevation with increasing number of coronary occlusions. IPC reduced infarct size in Göttingen minipigs (45 ± 10% without vs. 25 ± 13% of area at risk with IPC), whereas such cardioprotection was absent in Ossabaw minipigs (54 ± 11% vs. 50 ± 11%). ConclusionApparently, the block of signal transduction of IPC in Ossabaw minipigs occurs distal to the sarcolemma, where KATP channel activation still attenuates ST-segment elevation as it does in Göttingen minipigs.

The Infarct-Reducing Effect of the δ2 Opioid Receptor Agonist Deltorphin II: The Molecular Mechanism.

The search for novel drugs for the treatment of acute myocardial infarction and reperfusion injury of the heart is an urgent aim of modern pharmacology. Opioid peptides could be such potential drugs in this area. However, the molecular mechanism of the infarct-limiting effect of opioids in reperfusion remains unexplored. The objective of this research was to study the signaling mechanisms of the cardioprotective effect of deltorphin II in reperfusion. Rats were subjected to coronary artery occlusion (45 min) and reperfusion (2 h). The ratio of infarct size/area at risk was determined. This study indicated that the cardioprotective effect of deltorphin II in reperfusion is mediated via the activation of peripheral δ2 opioid receptor (OR), which is most likely localized in cardiomyocytes. We studied the role of guanylyl cyclase, protein kinase Cδ (PKCδ), phosphatidylinositol-3-kinase (PI3-kinase), extracellular signal-regulated kinase-1/2 (ERK1/2-kinase), ATP-sensitive K+-channels (KATP channels), mitochondrial permeability transition pore (MPTP), NO synthase (NOS), protein kinase A (PKA), Janus 2 kinase, AMP-activated protein kinase (AMPK), the large conductance calcium-activated potassium channel (BKCa-channel), reactive oxygen species (ROS) in the cardioprotective effect of deltorphin II. The infarct-reducing effect of deltorphin II appeared to be mediated via the activation of PKCδ, PI3-kinase, ERK1/2-kinase, sarcolemmal KATP channel opening, and MPTP closing.

δ2-Opioid Receptors as a Target in Designing New Cardioprotective Drugs: the Role of Protein Kinase C, AMPK, and Sarcolemmal KATP Channels

In rats anesthetized with α-chloralose, coronary artery occlusion (45 min) and reperfusion (120 min) were modeled. The selective δ2-opioid receptor agonist deltorphin II was administered 5 min before reperfusion. Protein kinase C inhibitor chelerythrine, AMP-activated protein kinase inhibitor compound C, and ATP-sensitive K+ channel blockers glibenclamide, 5-hydroxydecanoate, and HMR 1098 were administered 10 min before reperfusion. It was found that the infarct-limiting effect of deltorphin II is associated with activation of protein kinase C and opening of sarcolemmal ATP-sensitive K+ channel.

SUR2A as a base for cardioprotective therapeutic strategies.

ATP-sensitive K+ (KATP) channels link the metabolic state of the cell with membrane excitability and SUR2A serves as a regulatory subunit of sarcolemmal KATP channels. The aim of the present study was to review SUR2A-mediated cardioprotection. A related literature search in PubMed, Scopus, Web of Science, Google Scholar, and Science direct was performed. Levels of SUR2A regulate number of fully assembled KATP channels in the sarcolemma. Increased numbers of sarcolemmal KATP channels protect cardiomyocytes against different types of stress by improving the timing of KATP channels opening, but, also, by catalyzing ATP production in subsarcolemmal space. Fully-assembled sarcolemmal KATP channels protein complex contain ATP-producing enzymes in addition to channel subunits, SUR2A and Kir6.2. An increase in the number of fully-assembled channels results in increased levels of ATP-producing enzymes and subsarcolemmal ATP, which is beneficial in ischemia. Expression of SUR2A is regulated by diverse mechanisms, including AMPK, PI3K/Akt, and ERK1/2 as well as intracellular levels of NAD+/NADH and ATP. There are many compounds and treatments that can be used to regulate SUR2A and some of them seem to be clinically viable options. The most suitable medication to use to increase SUR2A and confer cardioprotection in the clinical setting seems to be nicotinamide. It is one of the safest compounds used in clinical practice and all pre-clinical studies demonstrated that it is an efficient cardioprotective agent. Taken all together, SUR2A-based cardioprotection is a likely efficient and safe cardioprotective strategy that can be quickly introduced into clinical practice.

Abstract 15558: Characterization of Sarcolemmal K Atp Channels in Human Ipsc-derived Cardiomyocytes

Background: The ATP-sensitive potassium channel (KATP) plays a key role in protecting heart muscle during metabolic challenges such as ischemia. KATP activation causes action potential shortening that reduces calcium entry and contraction thus reducing calcium overload induced damage and preserving energy reserves. Cardiomyocytes derived from human inducible pluripotent stem cell (hiPSC) have emerged as a model to study cardiac function, however there are few studies that have focused on KATP. Methods: In the present study, cardiomyocytes were either generated from hiPSC using heparin- based chemically defined media or purchased from Cellular Dynamics (iCells2). Expression of the pore-forming (Kir6.2) and regulatory (SUR1 & SUR2) subunits of the KATP channel during differentiation were assessed using western blot. KATP function was assessed by measuring the field potential duration (FPD) and spontaneous beat rate in a confluent monolayer using the Axion Maestro multielectrode array system. Cells were probed using the KATP activators P1075 and diazoxide, specific for SUR2 and SUR1, respectively. Results: We found that the pore-forming subunit of the sarcolemmal KATP channel (Kir6.2) was expressed in iPSC and maintained throughout the course of differentiation. Consistent with the typical composition of sarcolemmal KATP, we observe a significant increase of SUR2 but little SUR1 protein following Wnt inhibition. Functionally, the FPD is markedly reduced by P1075 in a concentration-dependent manner, with 24% reduction at 100 nM and 92 % reduction at 100 μM. Moreover, glibenclamide 10μM reduces FPD shortening confirming a role for KATP. Finally, we observe little change in FPD when cells are exposed to diazoxide (100 μM) consistent with reduced SUR1 protein levels. Conclusion: These results indicate that cardiomyocytes derived from human iPSC express the KATP channel composed of primarily the SUR2 isoform and suggest that iPSC derived cardiomyocytes would be an effective model for studying the role of KATP during metabolic challenges.

The Role of Natriuretic Peptides in the Regulation of Cardiac Tolerance to Ischemia/Reperfusion and Postinfarction Heart Remodeling.

In the past 10 years, mortality from acute myocardial infarction has not decreased despite the widespread introduction of percutaneous coronary intervention. The reason for this situation is the absence in clinical practice of drugs capable of preventing reperfusion injury of the heart with high efficiency. In this regard, noteworthy natriuretic peptides (NPs) which have the infarct-limiting effect, prevent reperfusion cardiac injury, prevent adverse post-infarction remodeling of the heart. Atrial natriuretic peptide does not have the infarct-reducing effect in rats with alloxan-induced diabetes mellitus. NPs have the anti-apoptotic and anti-inflammatory effects. There is indirect evidence that NPs inhibit pyroptosis and autophagy. Published data indicate that NPs inhibit reactive oxygen species production in cardiomyocytes, aorta, heart, kidney and the endothelial cells. NPs can suppress aldosterone, angiotensin II, endothelin-1 synthesize and secretion. NPs inhibit the effects aldosterone, angiotensin II on the post-receptor level through intracellular signaling events. NPs activate guanylyl cyclase, protein kinase G and protein kinase A, and reduce phosphodiesterase 3 activity. NO-synthase and soluble guanylyl cyclase are involved in the cardioprotective effect of NPs. The cardioprotective effect of natriuretic peptides is mediated via activation of kinases (AMPK, PKC, PI3 K, ERK1/2, p70s6 k, Akt) and inhibition of glycogen synthase kinase 3β. The cardioprotective effect of NPs is mediated via sarcolemmal KATP channel and mitochondrial KATP channel opening. The cardioprotective effect of brain natriuretic peptide is mediated via MPT pore closing. The anti-fibrotic effect of NPs may be mediated through inhibition TGF-β1 expression. Natriuretic peptides can inhibit NF-κB activity and activate GATA. Hemeoxygenase-1 and peroxisome proliferator-activated receptor γ may be involved in the infarct-reducing effect of NPs. NPs exhibit the infarct-limiting effect in patients with acute myocardial infarction. NPs prevent post-infarction remodeling of the heart. To finally resolve the question of the feasibility of using NPs in AMI, a multicenter, randomized, blind, placebo-controlled study is needed to assess the effect of NPs on the mortality of patients after AMI.

Improved adaptation to physical stress in mice overexpressing SUR2A is associated with changes in the pattern of Q-T interval

The purpose of this study was to determine whether increased expression of SUR2A, a regulatory subunit of sarcolemmal ATP-sensitive K+ (KATP) channels, improves adaptation to physical stress and regulates cardiac electrophysiology in physical stress. All experiments have been done on transgenic mice in which SUR2A expression was controlled by cytomegalovirus immediate-early (CMV) promoter (SUR2A) and their littermate wild-type controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR. Electrocardiogram (ECG) was monitored with telemetry. The physical adaptation to stress was elucidated using treadmill. We have found that SUR2A mice express 8.34 ± 0.20 times more myocardial SUR2A mRNA than WT (n = 8–18). The tolerated workload on exercise stress test was more than twofold higher in SUR2A than in WT (n = 5–7; P = 0.01). The pattern of Q-T interval from the beginning of the exercise test until drop point was as follows in the wild type: (1) increase in Q-T interval, (2) decrease in Q-T interval, (3) steady stage with a further decrease in Q-T interval, and (4) a sharp increase in Q-T interval. The pattern of Q-T interval was different in transgenic mice and the following stages have been observed: (1) increase in Q-T interval, (2) decrease in Q-T interval, and (3) prolonged steady-state stage with a slight decrease in Q-T interval. In SUR2A mice, no stage 4 (a sharp increase in Q-T interval) was observed. Based on the obtained results, we conclude that an increase in the expression of SUR2A improves adaptation to physical stress and physical endurance by increasing the number of sarcolemmal KATP channels and, by virtue of their channel activity, improving Ca2+ homeostasis in the heart.

Functional modulation of sarcolemmal KATP channels by atrial natriuretic peptide-elicited intracellular signaling in adult rabbit ventricular cardiomyocytes.

ATP-sensitive potassium (KATP) channels couple cell metabolic status to membrane excitability and are crucial for stress adaptation and cytoprotection in the heart. Atrial natriuretic peptide (ANP), a cardiac peptide important for cardiovascular homeostasis, also exhibits cytoprotective features including protection against myocardial ischemia-reperfusion injuries. However, how ANP modulates cardiac KATP channels is largely unknown. In the present study we sought to address this issue by investigating the role of ANP signaling in functional modulation of sarcolemmal KATP (sarcKATP) channels in ventricular myocytes freshly isolated from adult rabbit hearts. Single-channel recordings were performed in combination with pharmacological approaches in the cell-attached patch configuration. Bath application of ANP markedly potentiated sarcKATP channel activities induced by metabolic inhibition with sodium azide, whereas the KATP-stimulating effect of ANP was abrogated by selective inhibition of the natriuretic peptide receptor type A (NPR-A), cGMP-dependent protein kinase (PKG), reactive oxygen species (ROS), extracellular signal-regulated protein kinase (ERK)1/2, Ca2+/calmodulin-dependent protein kinase II (CaMKII), or the ryanodine receptor (RyR). Blockade of RyRs also nullified hydrogen peroxide (H2O2)-induced stimulation of sarcKATP channels in intact cells. Furthermore, single-channel kinetic analyses revealed that ANP enhanced the function of ventricular sarcKATP channels through destabilizing the long closures and facilitating the opening transitions, without affecting the single-channel conductance. In conclusion, here we report that ANP positively modulates the activity of ventricular sarcKATP channels via an intracellular signaling mechanism consisting of NPR-A, PKG, ROS, ERK1/2, CaMKII, and RyR2. This novel mechanism may regulate cardiac excitability and contribute to cytoprotection, in part, by opening myocardial KATP channels.

Effect of the Sarcolemmal KATP Channel Blocker HMR1098 on Arrhythmias Induced by Programmed Electrical Stimulation in Canine Old Myocardial Infarction Model: Comparison With Glibenclamide

Effect of the Sarcolemmal KATP Channel Blocker HMR1098 on Arrhythmias Induced by Programmed Electrical Stimulation in Canine Old Myocardial Infarction Model: Comparison With Glibenclamide

Role of sarcolemmal KATP channel in sevoflurane-induced maintenance of electrophysiological stability of ventricular myocardium in diabetic rats

Objective To evaluate the role of sarcolemmal ATP-sensitive potassium (sarcKATP) channel in sevoflurane-induced maintenance of electrophysiological stability of ventricular myocardium in diabetic rats. Methods Clean-grade healthy male Sprague-Dawley rats, aged 3 months, weighing 280-320 g, in which diabetes mellitus (DM) was induced by intraperitoneal streptozotocin 60 mg/kg and confirmed by blood glucose ≥16.7 mmol/L, were used in this study.Their hearts were excised after anesthesia and retrogradely perfused in a Langendorff apparatus at 4 weeks after establishing the DM model.Twenty-four Langendorff-perfused hearts were divided into 3 groups (n=8 each) using a random number table method: DM group (group D), DM plus sevoflurane group (group DS) and DM plus sevoflurane plus HMR-1098 group (group DSH). Another 8 Langendorff-perfused hearts of normal rats were selected as control group (group C). Hearts were perfused with 37 ℃ K-H solution via the aorta in each group, 15 min of equilibration later hearts were continuously perfused for 30 min with K-H solution in C and D groups, with K-H solution saturated with 2.5% sevoflurane in group DS, or with K-H solution saturated with 10 μmol/L HMR-1098 and 2.5% sevoflurane in group DSH.Monophasic action potential (MAP) duration at 50% and 90% repolarization (MAPD50 and MAPD90) in the endocardium and epicardium of the left ventricular anterior wall were recorded at 15 min of equilibration (T0) and 15 and 30 min of reperfusion (T1, 2), transmural dispersion of repolarization (TDR) was calculated.S1S2 program-controlled stimulation was performed at the end of perfusion to record the effective refractory period (ERP), ventricular arrhythmia (VA) induced and the longest pacing cycle length (PCL) of ventricular fibrillation threshold (VFT)induced.ERP/MAPD90 ratio was calculated. Results Compared with group C, TDR was significantly increased at T0, ERP/MADP90 ratio was decreased, the incidence of VA induced was increased, and the longest PCL of VFT induced was prolonged in group D (P<0.05). Compared with group D, TDR was significantly decreased at T2 in group DS (P<0.05), and ERP/MADP90 ratio was significantly increased, the incidence of VA induced was decreased, and the longest PCL of VFT induced was shortened in DS and DSH groups (P<0.05). TDR was significantly smaller at T2 in group DSH than in group DS (P<0.05). Conclusion sarcKATP channel is involved in sevoflurane-induced maintenance of electrophysiological stability of ventricular myocardium in diabetic rats. Key words: KATP channels; Anesthetics, inhalation; Diabetes mellitus; Cardiac electrophysiology

The trafficking protein, EHD2, positively regulates cardiac sarcolemmal KATP channel surface expression: role in cardioprotection.

ATP-sensitive K+ (KATP) channels uniquely link cellular energy metabolism to membrane excitability and are expressed in diverse cell types that range from the endocrine pancreas to neurons and smooth, skeletal, and cardiac muscle. A decrease in the surface expression of KATP channels has been linked to various disorders, including dysregulated insulin secretion, abnormal blood pressure, and impaired resistance to cardiac injury. In contrast, up-regulation of KATP channel surface expression may be protective, for example, by mediating the beneficial effect of ischemic preconditioning. Molecular mechanisms that regulate KATP channel trafficking are poorly understood. Here, we used cellular assays with immunofluorescence, surface biotinylation, and patch clamping to demonstrate that Eps15 homology domain-containing protein 2 (EHD2) is a novel positive regulator of KATP channel trafficking to increase surface KATP channel density. EHD2 had no effect on cardiac Na+ channels (Nav1.5). The effect is specific to EHD2 as other members of the EHD family-EHD1, EHD3, and EHD4-had no effect on KATP channel surface expression. EHD2 did not directly affect KATP channel properties as unitary conductance and ATP sensitivity were unchanged. Instead, we observed that the mechanism by which EHD2 increases surface expression is by stabilizing KATP channel-containing caveolar structures, which results in a reduced rate of endocytosis. EHD2 also regulated KATP channel trafficking in isolated cardiomyocytes, which validated the physiologic relevance of these observations. Pathophysiologically, EHD2 may be cardioprotective as a dominant-negative EHD2 mutant sensitized cardiomyocytes to ischemic damage. Our findings highlight EHD2 as a potential pharmacologic target in the treatment of diseases with KATP channel trafficking defects.-Yang, H. Q., Jana, K., Rindler, M. J., Coetzee, W. A. The trafficking protein, EHD2, positively regulates cardiac sarcolemmal KATP channel surface expression: role in cardioprotection.

KATP channel inhibition blunts electromechanical decline during hypoxia in left ventricular working rabbit hearts

Heart function is critically dependent upon the balance of energy production and utilization. Sarcolemmal ATP-sensitive potassium channels (KATP channels) in cardiac myocytes adjust contractile function to compensate for the level of available energy. Understanding the activation of KATP channels in working myocardium during high-stress situations is crucial to the treatment of cardiovascular disease, especially ischaemic heart disease. Using a new optical mapping approach, we measured action potentials from the surface of excised contracting rabbit hearts to assess when sarcolemmal KATP channels were activated during physiologically relevant workloads and during gradual reductions in myocardial oxygenation. We demonstrate that left ventricular pressure is closely linked to KATP channel activation and that KATP channel inhibition with a low concentration of tolbutamide prevents electromechanical decline when oxygen availability is reduced. As a result, KATP channel inhibition probably exacerbates a mismatch between energy demand and energy production when myocardial oxygenation is low. Sarcolemmal ATP-sensitive potassium channel (KATP channel) activation in isolated cells is generally understood, although the relationship between myocardial oxygenation and KATP activation in excised working rabbit hearts remains unknown. We optically mapped action potentials (APs) in excised rabbit hearts to test the hypothesis that hypoxic changes would be more severe in left ventricular (LV) working hearts (LWHs) than Langendorff (LANG) perfused hearts. We further hypothesized that KATP inhibition would prevent those changes. Optical APs were mapped when measuring LV developed pressure (LVDP), coronary flow rate and oxygen consumption in LANG and LWHs. Hearts were paced to increase workload and perfusate was deoxygenated to study the effects of myocardial hypoxia. A subset of hearts was perfused with 1μm tolbutamide (TOLB) to identify the level of AP duration (APD) shortening attributed to KATP channel activation. During sinus rhythm, APD was shorter in LWHs compared to LANG hearts. APD in both LWHs and LANG hearts dropped steadily during deoxygenation. With TOLB, APDs in LWHs were longer at all workloads and APD reductions during deoxygenation were blunted in both LWHs and LANG hearts. At 50% perfusate oxygenation, APD and LVDP were significantly higher in LWHs perfused with TOLB (199±16ms; 92±5.3mmHg) than in LWHs without TOLB (109±14ms, P=0.005; 65±6.5mmHg, P=0.01). Our results indicate that KATP channels are activated to a greater extent in perfused hearts when the LV performs pressure-volume work. The results of the present study demonstrate the critical role of KATP channels in modulating myocardial function over a wide range of physiological conditions.

Electrophysiology of Hypokalemia and Hyperkalemia.

Electrophysiology of Hypokalemia and Hyperkalemia.

Non-cell autonomous cues for enhanced functionality of human embryonic stem cell-derived cardiomyocytes via maturation of sarcolemmal and mitochondrial KATP channels.

Human embryonic stem cells (hESCs) is a potential unlimited ex vivo source of ventricular (V) cardiomyocytes (CMs), but hESC-VCMs and their engineered tissues display immature traits. In adult VCMs, sarcolemmal (sarc) and mitochondrial (mito) ATP-sensitive potassium (KATP) channels play crucial roles in excitability and cardioprotection. In this study, we aim to investigate the biological roles and use of sarcKATP and mitoKATP in hESC-VCM. We showed that SarcIK, ATP in single hESC-VCMs was dormant under baseline conditions, but became markedly activated by cyanide (CN) or the known opener P1075 with a current density that was ~8-fold smaller than adult; These effects were reversible upon washout or the addition of GLI or HMR1098. Interestingly, sarcIK, ATP displayed a ~3-fold increase after treatment with hypoxia (5% O2). MitoIK, ATP was absent in hESC-VCMs. However, the thyroid hormone T3 up-regulated mitoIK, ATP, conferring diazoxide protective effect on T3-treated hESC-VCMs. When assessed using a multi-cellular engineered 3D ventricular cardiac micro-tissue (hvCMT) system, T3 substantially enhanced the developed tension by 3-folds. Diazoxide also attenuated the decrease in contractility induced by simulated ischemia (1% O2). We conclude that hypoxia and T3 enhance the functionality of hESC-VCMs and their engineered tissues by selectively acting on sarc and mitoIK, ATP.

Abstract 286: Role of ATP-sensitive Potassium Channel Openers in Prevention of Atrial Fibrillation

Introduction: The ATP-sensitive potassium (K ATP ) channel dysfunction causes susceptibility to adrenergic atrial fibrillation (AF). However, the therapeutic efficacy of K ATP activation in primary prevention of AF is not known. We hypothesized that K ATP channel opening drugs prevent AF with effective metabolic and mechanosensitive gating of K ATP channels and preserving electro-anatomical stability in atria by regulating oxidative and metabolic states. Methods: This hypothesis was tested in a novel mouse model of AF, cardiac specific LKB1 knockout (KO) mice. Male and female LKB1 KO mice were treated with K ATP channel openers, nicorandil (15 mg/kg/day) and diazoxide (10 mg/kg/day). Control group included untreated littermates of the study group. Incidence of AF, structural and electrophysiological property of atria and sex-based differences were analyzed at the 3 months of age in all groups. Results: The incidence of spontaneous AF was significant reduced in LKB1 KO male mice with nicorandil (0%, n=5) and diazoxide (33%, n=6) treatment compare to untreated mice (84.6%, n=13) (p&lt;0.05). The treatment was also effective in female LKB1 KO mice as AF occurred in 37.5% of nicorandil (n=8) and 40% of diazoxide (n=5) (p&lt;0.05) treated mice as oppose to 71% of untreated mice (n=24). The K ATP openers, particularly nicorandil, were more effective in male mice preventing AF. There was 100% risk reduction with nicorandil in male mice compare to 39% with diazoxide. Nicorandil demonstrated 52% risk reduction in female mice while it was 56% with diazoxide treatment. Prevention of AF was associated with preservation of atrial structural and electrical property including size, heart rate and conduction intervals. Biatrial enlargement was significantly prevented by K ATP openers compare to untreated mice. Incidence of AF was significantly higher in male mice than female with or without treatment. Conclusions: Activation of sarcolemmal and mitochondrial K ATP channels prevents AF by preserving electro-anatomical property of atria and decreasing susceptibility to AF. Metabolic regulation of K ATP is essential in AF. Thus, the K ATP openers are novel upstream therapy for primary prevention of AF in vulnerable population.

Plasticity of sarcolemmal KATP channel surface expression: relevance during ischemia and ischemic preconditioning.

Myocardial ischemia remains the primary cause of morbidity and mortality in the United States. Ischemic preconditioning (IPC) is a powerful form of endogenous protection against myocardial infarction. We studied alterations in KATP channels surface density as a potential mechanism of the protection of IPC. Using cardiac-specific knockout of Kir6.2 subunits, we demonstrated an essential role for sarcolemmal KATP channels in the infarct-limiting effect of IPC in the mouse heart. With biochemical membrane fractionation, we demonstrated that sarcolemmal KATP channel subunits are distributed both to the sarcolemma and intracellular endosomal compartments. Global ischemia causes a loss of sarcolemmal KATP channel subunit distribution and internalization to endosomal compartments. Ischemia-induced internalization of KATP channels was prevented by CaMKII inhibition. KATP channel subcellular redistribution was also observed with immunohistochemistry. Ischemic preconditioning before the index ischemia reduced not only the infarct size but also prevented KATP channel internalization. Furthermore, not only did adenosine mimic IPC by preventing infarct size, but it also prevented ischemia-induced KATP channel internalization via a PKC-mediated pathway. We show that preventing endocytosis with dynasore reduced both KATP channel internalization and strongly mitigated infarct development. Our data demonstrate that plasticity of KATP channel surface expression must be considered as a potentially important mechanism of the protective effects of IPC and adenosine.

Effects of ATP-sensitive potassium channel blockers on vascular hyporeactivity, mesenteric blood flow, and survival in lipopolysaccharide-induced septic shock model.

In this study, the possible therapeutic effects of various ATP-sensitive potassium channel (KATP) blockers (glibenclamide, repaglinide, 5-HD, HMR-1098) have been tested in experimental septic shock model. Rats were given lipopolysaccharide (1 mg·kg(-1)) to create experimental shock model and 4 h later, under 400 mg·kg(-1) chloral hydrate anesthesia, parameters such as blood pressure, mesenteric blood flow, the response of mesenteric circulation to phenylephrine (vasoconstrictor stimulation), and organ and oxidative damage were analyzed. Also 75 mg·kg(-1) lethal dose of lipopolysaccharide was given to mice and effects of KATP blockers on survival have been tested. Non-selective blocker glibenclamide with sulphonylurea structure and sarcolemmal KATP channel blocker HMR-1098, which have the similar chemical structure, have improved the pathological parameters such as decrease in mesenteric blood flow, vascular hyporeactivity, but could not prevent the decrease in blood pressure, and oxidative and organ damage that were observed in the shock model. Also, both blockers have decreased the mortality rate from 80% to 40%-50%. Similar (preventive) therapeutic effects were not observed with non-selective blocker repaglinide and mitochondrial KATP channel blocker 5-HD, which were non-sulphonylurea structure. As a result, only KATP channel blockers that have sulphonylurea structure can be a new therapeutic approach in septic shock.