Lukas J. Motloch

Connexin 43 acts as a cytoprotective mediator of signal transduction by stimulating mitochondrial KATP channels in mouse cardiomyocytes

Potassium (K+) channels in the inner mitochondrial membrane influence cell function and survival. Increasing evidence indicates that multiple signaling pathways and pharmacological actions converge on mitochondrial ATP-sensitive K+ (mitoKATP) channels and PKC to confer cytoprotection against necrotic and apoptotic cell injury. However, the molecular structure of mitoKATP channels remains unresolved, and the mitochondrial phosphoprotein(s) that mediate cytoprotection by PKC remain to be determined. As mice deficient in the main sarcolemmal gap junction protein connexin 43 (Cx43) lack this cytoprotection, we set out to investigate a possible link among mitochondrial Cx43, mitoKATP channel function, and PKC activation. By patch-clamping the inner membrane of subsarcolemmal murine cardiac mitochondria, we found that genetic Cx43 deficiency, pharmacological connexin inhibition by carbenoxolone, and Cx43 blockade by the mimetic peptide 43GAP27 each substantially reduced diazoxide-mediated stimulation of mitoKATP channels. Suppression of mitochondrial Cx43 inhibited mitoKATP channel activation by PKC. MitoKATP channels of interfibrillar mitochondria, which do not contain any detectable Cx43, were insensitive to both PKC activation and diazoxide, further demonstrating the role of Cx43 in mitoKATP channel stimulation and the compartmentation of mitochondria in cell signaling. Our results define a role for mitochondrial Cx43 in protecting cardiac cells from death and provide a link between cytoprotective stimuli and mitoKATP channel opening, making Cx43 an attractive therapeutic target for protection against cell injury.

Cardiac arrest due to long QT syndrome associated with excessive consumption of energy drinks

Amphetamines 1000 Negative Barbiturates 300 Negative Benzodiazepines 300 Negative Cannabinoids 50 Negative Cocaine 300 Negative MDMA 500 Negative Metamphetamine 1000 Negative Methadone 300 Negative The congenital form of long QT syndrome is characterized by a prolonged QT interval in the electrocardiogram (ECG) and is complicated by episodes of polymorphic ventricular tachycardia known as torsades de pointes (TdP). Patients with long QT syndrome 1 (LQTS-1) typically may suffer cardiac arrest during exercise. Based on these observations beta-blocker therapy is recommended in these patients to reduce the maximal heart rate and blunt the effects of adrenaline. Energy drinks contain high doses of taurine (an amino acid), caffeine and glucuronolactone (a glucose metabolite), neither of which is considered to have significant toxicity. We report a case of a 22 year old female with out of hospital cardiac arrest (OHCA) due to initial torsades de pointes tachycardia secondary degenerating to ventricular fibrillation. Sudden cardiac death occurred without prodrome in a discotheque. Basic life support was performed immediately. After 15 minutes of resuscitation with fractionated administration of 3 mg adrenaline return of spontaneous circulation (ROSC) could be achieved after the patient received five 360 Joule shocks by the emergency medical services personnel. Initial ECG showed torsades de pointes tachycardia, which degenerated during resuscitation to ventricular fibrillation. After ROSC the patient was admitted to our intensive care unit. Acute cardiac catheterization excluded coronary macroangiopathy or coronary anomalies. Cardiac ventriculography revealed a normal ejection fraction of 69. Echocardiography showed normal cardiac function without any pathologic pattern. Furthermore, no pericardial effusion was found. Results of a urinary screen for drug or alcohol misuse were negative (Table 1). Potassium level at admission was normal (4.4 mmol/l). Abnormal

Postprocedural Atrial Fibrillation After Transcatheter Aortic Valve Implantation Versus Surgical Aortic Valve Replacement

BACKGROUND Transcatheter aortic valve implantation (TAVI) represents an alternative option for elderly patients with severe aortic valve stenosis who are denied surgical aortic valve replacement (SAVR) because of high perioperative risk. The impact of TAVI on postprocedural atrial fibrillation is undefined. METHODS In a single-center analysis, we assessed clinical data, preoperative risk scores (Society for Thoracic Surgeons score, logistic European System for Cardiac Operative Risk Evaluation), preprocedural electrocardiograms, and 72-hour postprocedural rhythm monitoring of 170 patients undergoing TAVI (n=84) or SAVR (n=86). In a subanalysis, transapical (n=43) and transfemoral TAVI (n=41) were compared. RESULTS Expectedly, TAVI patients were significantly older, presented with more severe symptoms, had higher Society for Thoracic Surgeons score, higher logistic European System for Cardiac Operative Risk Evaluation score, and revealed more frequently intermittent atrial fibrillation compared with SAVR patients. Despite this more compromised health state, prevalence of postprocedural atrial fibrillation was significantly lower in the TAVI group (6.0%, versus 33.7% after SAVR, p<0.05). More than two thirds of TAVI patients but no SAVR patient with atrial fibrillation in preprocedural electrocardiograms had stable sinus rhythm during 72-hour postprocedural monitoring. Notably, no atrial fibrillation was observed after transfemoral TAVI. Whereas atrial fibrillation onset in the SAVR group predominantly occurred on postoperative day 3, atrial fibrillation onset after transapical TAVI was obtained within the first 24 hours after the intervention. CONCLUSIONS Our results indicate that TAVI, compared with SAVR, reduces the risk of periprocedural atrial fibrillation. Furthermore, preprocedural atrial fibrillation may be converted into sinus rhythm particularly after transfemoral TAVI, suggesting an impact of decreased intracardiac pressures in the absence of adverse periprocedural factors that might promote atrial fibrillation.

Clinical Impact of Atrial Fibrillation in Patients with Pulmonary Hypertension

Background Pulmonary hypertension (PH) is associated with progressive impairment of right ventricular function, reduced exercise capacity and a poor prognosis. Little is known about the prevalence, clinical manifestation and impact of atrial fibrillation (AF) on cardiac function in PH. Methods In a four year single-centre retrospective analysis 225 patients with confirmed PH of various origins were enrolled to investigate the prevalence of AF, and to assess the clinical manifestation, 6-minute walk distance, NT-proBNP levels, echocardiographic parameters and hemodynamics obtained by right heart catheterization in PH with AF. Results AF was prevalent in 31.1%. In patients with PH and AF, parameters of clinical deterioration (NYHA/WHO functional class, 6-minute walk distance, NT-proBNP levels) and renal function were significantly compromised compared to patients with PH and sinus rhythm (SR). In the total PH cohort and in PH not related to left heart disease occurrence of AF was associated with an increase of right atrial pressure (RAP) and right atrial dilatation. While no direct association was found between pulmonary artery pressure (PAP) and AF in these patients, right ventricular function was reduced in AF, indicating more advanced disease. In PH due to left heart failure the prevalence of AF was particularly high (57.7% vs. 23.1% in other forms of PH). In this subgroup, left atrial dilatation, increase of pulmonary capillary wedge pressure, PAP and RAP were more pronounced in AF than in SR, suggesting that more marked backward failure led to AF in this setting. Conclusion PH is associated with increased prevalence of AF. Occurrence of AF in PH indicates clinical deterioration and more advanced disease.

Glycogen synthase kinase 3β transfers cytoprotective signaling through connexin 43 onto mitochondrial ATP-sensitive K+ channels

Despite compelling evidence supporting key roles for glycogen synthase kinase 3β (GSK3β), mitochondrial adenosine triphosphate-sensitive K+ (mitoKATP) channels, and mitochondrial connexin 43 (Cx43) in cytoprotection, it is not clear how these signaling modules are linked mechanistically. By patch-clamping the inner membrane of murine cardiac mitochondria, we found that inhibition of GSK3β activated mitoKATP. PKC activation and protein phosphatase 2a inhibition increased the open probability of mitoKATP channels through GSK3β, and this GSK3β signal was mediated via mitochondrial Cx43. Moreover, (i) PKC-induced phosphorylation of mitochondrial Cx43 was reduced in GSK3β-S9A mice; (ii) Cx43 and GSK3β proteins associated in mitochondria; and (iii) SB216763-mediated reduction of infarct size was abolished in Cx43 KO mice in vivo, consistent with the notion that GSK3β inhibition results in mitoKATP opening via mitochondrial Cx43. We therefore directly targeted mitochondrial Cx43 by the Cx43 C-terminal binding peptide RRNYRRNY for cardioprotection, circumventing further upstream pathways. RRNYRRNY activated mitoKATP channels via Cx43. We directly recorded mitochondrial Cx43 channels that were activated by RRNYRRNY and blocked by the Cx43 mimetic peptide 43GAP27. RRNYRRNY rendered isolated cardiomyocytes in vitro and the heart in vivo resistant to ischemia/reperfusion injury, indicating that mitochondrial Cx43- and/or mitoKATP-mediated reduction of infarct size was not undermined by RRNYRRNY-related opening of sarcolemmal Cx43 channels. Our results demonstrate that GSK3β transfers cytoprotective signaling through mitochondrial Cx43 onto mitoKATP channels and that Cx43 functions as a channel in mitochondria, being an attractive target for drug treatment against cardiomyocyte injury.

Effects of KCNE2 on HCN isoforms: distinct modulation of membrane expression and single channel properties.

Hyperpolarization-activated cation (HCN) channels give rise to an inward current with similar but not identical characteristics compared with the pacemaker current (I(f)), suggesting that HCN channel function is modulated by regulatory beta-subunits in native tissue. KCNE2 has been proposed to serve as a beta-subunit of HCN channels; however, available data remain contradictory. To further clarify this situation, we therefore analyzed the effect of KCNE2 on whole cell currents, single channel properties, and membrane protein expression of all cardiac HCN isoforms in the CHO cell system. On the whole cell level, current densities of all HCN isoforms were significantly increased by KCNE2 without altering voltage dependence or current reversal. While these results correlated well with the KCNE2-mediated 2.2-fold and 1.6-fold increases of membrane protein levels of HCN2 and HCN4, respectively, no effect of KCNE2 on HCN1 expression was obtained. All HCN subtypes displayed faster activation kinetics upon coexpression with KCNE2. Most importantly, for the first time, we demonstrated modulation of single channel function by KCNE2, thus supporting direct functional interaction with HCN subunits. In the presence of KCNE2, the single channel amplitudes and conductance of HCN1, HCN2, and HCN4 were significantly increased versus control recordings. Mean open time was significantly increased in cells coexpressing HCN2 + KCNE2, whereas it was unaffected in HCN1 + KCNE2 cotransfected cells and reduced in HCN4 + KCNE2 cotransfected cells compared with the respective HCN subunits alone. Thus, we demonstrate KCNE2-mediated distinct effects on HCN membrane expression and direct functional modulation of HCN isoforms, further supporting that KCNE2 surves as a regulatory beta-subunit of HCN channels.

By Regulating Mitochondrial Ca2+-Uptake UCP2 Modulates Intracellular Ca2+.

Introduction The possible role of UCP2 in modulating mitochondrial Ca2+-uptake (mCa2+-uptake) via the mitochondrial calcium uniporter (MCU) is highly controversial. Methods Thus, we analyzed mCa2+-uptake in isolated cardiac mitochondria, MCU single-channel activity in cardiac mitoplasts, dual Ca2+-transients from mitochondrial ((Ca2+)m) and intracellular compartment ((Ca2+)c) in the whole-cell configuration in cardiomyocytes of wild-type (WT) and UCP2-/- mice. Results Isolated mitochondria showed a Ru360 sensitive mCa2+-uptake, which was significantly decreased in UCP2-/- (229.4±30.8 FU vs. 146.3±23.4 FU, P<0.05). Single-channel registrations confirmed a Ru360 sensitive voltage-gated Ca2+-channel in mitoplasts, i.e. mCa1, showing a reduced single-channel activity in UCP2-/- (Po,total: 0.34±0.05% vs. 0.07±0.01%, P<0.05). In UCP2-/- cardiomyocytes (Ca2+)m was decreased (0.050±0.009 FU vs. 0.021±0.005 FU, P<0.05) while (Ca2+)c was unchanged (0.032±0.002 FU vs. 0.028±0.004 FU, P>0.05) and transsarcolemmal Ca2+-influx was inhibited suggesting a possible compensatory mechanism. Additionally, we observed an inhibitory effect of ATP on mCa2+-uptake in WT mitoplasts and (Ca2+)m of cardiomyocytes leading to an increase of (Ca2+)c while no ATP dependent effect was observed in UCP2-/-. Conclusion Our results indicate regulatory effects of UCP2 on mCa2+-uptake. Furthermore, we propose, that previously described inhibitory effects on MCU by ATP may be mediated via UCP2 resulting in changes of excitation contraction coupling.

UCP3 Regulates Single-Channel Activity of the Cardiac mCa1.

Mitochondrial Ca2+ uptake (mCa2+ uptake) is thought to be mediated by the mitochondrial Ca2+ uniporter (MCU). UCP2 and UCP3 belong to a superfamily of mitochondrial ion transporters. Both proteins are expressed in the inner mitochondrial membrane of the heart. Recently, UCP2 was reported to modulate the function of the cardiac MCU related channel mCa1. However, the possible role of UCP3 in modulating cardiac mCa2+ uptake via the MCU remains inconclusive. To understand the role of UCP3, we analyzed cardiac mCa1 single-channel activity in mitoplast-attached single-channel recordings from isolated murine cardiac mitoplasts, from adult wild-type controls (WT), and from UCP3 knockout mice (UCP3–/–). Single-channel registrations in UCP3−/− confirmed a murine voltage-gated Ca2+ channel, i.e., mCa1, which was inhibited by Ru360. Compared to WT, mCa1 in UCP3−/− revealed similar single-channel characteristics. However, in UCP3−/− the channel exhibited decreased single-channel activity, which was insensitive to adenosine triphosphate (ATP) inhibition. Our results suggest that beyond UCP2, UCP3 also exhibits regulatory effects on cardiac mCa1/MCU function. Furthermore, we speculate that UCP3 might modulate previously described inhibitory effects of ATP on mCa1/MCU activity as well.

Postoperative ergometry-guided programming does not prevent T-wave oversensing and inappropriate shocks in S-ICD patients: LARBIG et al.

T‐wave oversensing (TWOS) is a feared complication after subcutaneous implantable cardioverter‐defibrillator (S‐ICD) implantation, potentially leading to inappropriate shocks (IS) with tremendous impact on quality of life.

Diagnose & Therapie der diastolischen Herzinsuffizienz

ZusammenfassungIn den letzten Jahren hat sich herausgestellt, dass die diastolische Herzinsuffizienz sehr viel häufiger auftritt als vermutet. Bei mehr als 50 % der chronisch herzinsuffizienten Patienten ist vor allem die diastolische Funktion beeinträchtigt, während die Pumpfunktion erhalten ist. Hauptursache dafür ist eine linksventrikuläre Hypertrophie, oft infolge einer arteriellen Hypertonie. Aufgrund der hohen Morbidität und Mortalität muss die Diagnose möglichst früh gestellt werden. Die Grunderkrankung sollte nach Möglichkeit kausal behandelt werden. Bisher wurden Patienten mit diastolischer Herzinsuffizienz aber oft explizit von Therapiestudien ausgeschlossen. Daher gibt es derzeit zu wenige Daten für eine evidenzbasierte Behandlung.