A multiplex PCR strategy to screen for known mutations in families with sudden cardiac death burden.

Ventricular tachyarrythmia occurring in ischemic heart disease, dilated/hypertrophic cardiomyopathies or rare monogenic mutations of cardiac ion channels or associated proteins belong to the most frequent causes of sudden cardiac death (SCD). In further decades, next generation sequencing and bioinformatic analysis will become the gold standard of SCD risk stratification. At the moment, Sanger-sequencing is still obligatory in genetic diagnosis. A multiplex polymerase chain reaction (PCR) assay detecting eight SCD mutations in one reaction-tube was developed. To test the general validity of the assay, it was used with 12 patients, who had one or two of the eight mutations (LMNA, p.V256V; SCN5A, p.R1583C; RYR2, p.G1885E; MYH7, V606M; DSG2, p.T335A; KCNJ8, p.S422L; MYBPC, p.E441K; TNNT2, A38V). Thereafter, we tested the multiplex assay in a real diagnostic environment within a high risk family of several past SCD cases. This method allows efficient discrimination of multiple mutations by allele-specific PCR with standard PCR conditions. It relies on obtaining a PCR product specific to the mutation or wildtype-using primers that have the 3'end base complementary to the DNA template site, i.e. a specific primer only permits amplification to take place when its 3'terminal nucleotide matches with its target sequence. The PCR products are further analyzed by length, with Tape Station®(Agilent Technologies, Germany), a high-fidelity capillary chromatography test. The novel multiplex PCR assay strategy could be a good additional test used for SCD risk stratification. Advantages of the test are high velocity and ease of implementation, low price and flexibility of application within cardiomyopathy families for screening purposes.

[Consensus statement: Management of oral anticoagulation for stroke prevention in patients with nonvalvular atrial fibrillation]. / Konsensuspapier: Schlaganfallprophylaxe bei Patienten mit nichtvalvulärem Vorhofflimmern.

With the introduction of edoxaban last year in Germany, four nonvitamin K antagonist oral anticoagulants are now available for stroke prevention in patients with nonvalvular atrial fibrillation. These novel oral anticoagulants (NOAC) represent an attractive new option compared to vitamin K antagonists (e.g., warfarin or phenprocoumon) due to simple use and fewer interactions with other drugs or food. Therefore, no INR monitoring and dosage adjustments are required for NOAC. The compelling clinical advantage of NOAC is the dramatic risk reduction of hemorhagic stroke and intracranial bleeding compared to current standard. In addition, total mortality is significantly reduced by 10 %. These effects are demonstrated for all four NOAC (dabigatran, rivaroxaban, apixaban and edoxaban). Therefore, current national and international guidelines recommend NOAC as the preferred option or at least as an attractive alternative compared to the former standard of vitamin K antagonists. The economic impact and reimbursement by Statutory Health Insurance (GKV) is of major importance for treatment in an outpatient setting. For apixaban and edoxaban, an additional benefit was granted by the institution of G­BA and IQWiG in this clinical setting, whereas dabigatran and rivaroxaban were not assessed due to market entrance prior to 2011 before the AMNOG procedure was initiated. The members of this consensus paper recommend NOAC as the preferred option for patients with nonvalvular atrial fibrillation who are currently not treated with anticoagulant drugs in spite of clear indication for anticoagulation. For new patients with nonvalvular fibrillation, it should be decided on an individual basis which treatment option is adequate for the patient with their respective comorbidities.

Inhibition of Cardiac Kir Current (IK1) by Protein Kinase C Critically Depends on PKCß and Kir2.2.

BACKGROUND: Cardiac inwardly rectifying Kir current (IK1) mediates terminal repolarisation and is critical for the stabilization of the diastolic membrane potential. Its predominant molecular basis in mammalian ventricle is heterotetrameric assembly of Kir2.1 and Kir2.2 channel subunits. It has been shown that PKC inhibition of IK1 promotes focal ventricular ectopy. However, the underlying molecular mechanism has not been fully elucidated to date. METHODS AND RESULTS: In the Xenopus oocyte expression system, we observed a pronounced PKC-induced inhibition of Kir2.2 but not Kir2.1 currents. The PKC regulation of Kir2.2 could be reproduced by an activator of conventional PKC isoforms and antagonized by pharmacological inhibition of PKCß. In isolated ventricular cardiomyocytes (rat, mouse), pharmacological activation of conventional PKC isoforms induced a pronounced inhibition of IK1. The PKC effect in rat ventricular cardiomyocytes was markedly attenuated following co-application of a small molecule inhibitor of PKCß. Underlining the critical role of PKCß, the PKC-induced inhibition of IK1 was absent in homozygous PKCß knockout-mice. After heterologous expression of Kir2.1-Kir2.2 concatemers in Xenopus oocytes, heteromeric Kir2.1/Kir2.2 currents were also inhibited following activation of PKC. CONCLUSION: We conclude that inhibition of cardiac IK1 by PKC critically depends on the PKCß isoform and Kir2.2 subunits. This regulation represents a potential novel target for the antiarrhythmic therapy of focal ventricular arrhythmias.

Prediction and personalised treatment of atrial fibrillation-stroke prevention: consolidated position paper of CVD professionals.

Atrial fibrillation (AF) is one of the major morbidity and health economic factors in Europe and often associated with several co-morbidities. This paper (1) underlines the importance of highly professional AF management utilising a multi-disciplinary expertise, especially considering the role of AF regarding the stroke risk and prevention, (2) demonstrates the consolidated position of CVD professionals and (3) emphasises those research aspects that could deepen the understanding of the emergence and the treatment of AF and therefore helps to provide a personalised preventive and more effective management of AF. Specialised calls are considered for that within the new European Programme 'Horizon 2020'.

Inhibition of cardiac Kir2.1-2.3 channels by beta3 adrenoreceptor antagonist SR 59230A.

Kir2.x channels form the molecular basis of cardiac I(K1) current and play a major role in cardiac electrophysiology. However, there is a substantial lack of selective Kir2 antagonists. We found the ß(3)-adrenoceptor antagonist SR59230A to be an inhibitor of Kir2.x channels. Therefore, we characterized the effects of SR59230A on Kir2.x and other relevant cardiac potassium channels. Cloned channels were expressed in the Xenopus oocyte expression system and measured with the double-microelectrode voltage clamp technique. SR59230A inhibited homomeric Kir2.1 channels with an IC(50) of 33µM. Homomeric Kir2.2 and Kir2.3 channels and Kir2.x heteromers were also inhibited by SR59230A with similar potency. In contrast, no relevant inhibitory effects of SR59230A were found in cardiac Kv1.5, Kv4.3 and KvLQT1/minK channels. In hERG channels, SR59230A only induced a weak inhibition at a high concentration. These findings establish SR59230A as a novel inhibitor of Kir2.1-2.3 channels with a favorable profile with respect to additional effects on other cardiac repolarizing potassium channels.

Cardiovascular ion channels as a molecular target of flavonoids.

Flavonoids are a class of naturally occurring polyphenols abundant in edibles and beverages of plant origin. Epidemiological studies consistently associate high flavonoid intake with a reduced risk for the development of cardiovascular diseases. So far these beneficial effects have been mainly attributed to nonspecific antioxidant and antiinflammatory properties. However, there is an increasing body of evidence that flavonoids specifically target molecular structures including cardiovascular ion channels. Playing a pivotal role in the regulation of vascular tone and cardiac electric activity, ion channels represent a major target for the induction of antihypertensive and cardioprotective effects. Thus, pharmacological properties of flavonoids on cardiovascular ion channels, ion currents and tissue preparations are being increasingly addressed in experimental studies. Whereas it has become clear that cardiovascular ion channels represent an important molecular target of flavonoids, the published data have not yet been systematically reviewed.

Multiple mechanisms of hERG liability: K+ current inhibition, disruption of protein trafficking, and apoptosis induced by amoxapine.

The antidepressant amoxapine has been linked to cases of QT prolongation, acute heart failure, and sudden death. Inhibition of cardiac hERG (Kv11.1) potassium channels causes prolonged repolarization and is implicated in apoptosis. Apoptosis in association with amoxapine has not yet been reported. This study was designed to investigate amoxapine effects on hERG currents, hERG protein trafficking, and hERG-associated apoptosis in order to elucidate molecular mechanisms underlying cardiac side effects of the drug. hERG channels were expressed in Xenopus laevis oocytes and HEK 293 cells, and potassium currents were recorded using patch clamp and two-electrode voltage clamp electrophysiology. Protein trafficking was evaluated in HEK 293 cells by Western blot analysis, and cell viability was assessed in HEK cells by immunocytochemistry and colorimetric MTT assay. Amoxapine caused acute hERG blockade in oocytes (IC(50) = 21.6 microM) and in HEK 293 cells (IC(50) = 5.1 microM). Mutation of residues Y652 and F656 attenuated hERG blockade, suggesting drug binding to a receptor inside the channel pore. Channels were mainly blocked in open and inactivated states, and voltage dependence was observed with reduced inhibition at positive potentials. Amoxapine block was reverse frequency-dependent and caused accelerated and leftward-shifted inactivation. Furthermore, amoxapine application resulted in chronic reduction of hERG trafficking into the cell surface membrane (IC(50) = 15.3 microM). Finally, the antidepressant drug triggered apoptosis in cells expressing hERG channels. We provide evidence for triple mechanisms of hERG liability associated with amoxapine: (1) direct hERG current inhibition, (2) disruption of hERG protein trafficking, and (3) induction of apoptosis. Further experiments are required to validate a specific pro-apoptotic effect mediated through blockade of hERG channels.

Biophysical characterization of KCNQ1 P320 mutations linked to long QT syndrome 1.

Hereditary long QT syndrome (LQTS) is a cardiovascular disorder characterized by prolongation of the QT interval on the surface ECG and a high risk for arrhythmia-related sudden death. Mutations in a cardiac voltage-gated potassium channel, KCNQ1, account for the most common form of LQTS, LQTS1. The objective of this study was the characterization of a novel KCNQ1 mutation linked to LQTS. Electrophysiological properties and clinical features were determined and compared to characteristics of a different mutation at the same position. Single-strand conformation polymorphism analysis followed by direct sequencing was performed to screen LQTS genes for mutations. A novel missense mutation in the KCNQ1 gene, KCNQ1 P320H, was identified in the index patient presenting with recurrent syncope and aborted sudden death triggered by physical stress and swimming. Electrophysiological analyses of KCNQ1 P320H and the previously reported KCNQ1 P320A mutation indicate that both channels are non-functional and suppress wild type I(Ks) in a dominant-negative fashion. Based on homology modeling of the KCNQ1 channel pore region, we speculate that the proline residue at position 320 limits flexibility of the outer pore and is required to maintain the functional architecture of the selectivity filter/pore helix arrangement. Our observations on the KCNQ1 P320H mutation are consistent with previous studies indicating that pore mutations in potassium channel alpha-subunits are associated with more severe electrophysiological and clinical phenotypes than mutations in other regions of these proteins. This study emphasizes the significance of mutation screening for diagnosis, risk-assessment, and mutation-site specific management in LQTS patients.

Biophysical properties of zebrafish ether-à-go-go related gene potassium channels.

The zebrafish is increasingly recognized as an animal model for the analysis of hERG-related diseases. However, functional properties of the zebrafish orthologue of hERG have not been analyzed yet. We heterologously expressed cloned ERG channels in Xenopus oocytes and analyzed biophysical properties using the voltage clamp technique. zERG channels conduct rapidly activating and inactivating potassium currents. However, compared to hERG, the half-maximal activation voltage of zERG current is shifted towards more positive potentials and the half maximal steady-state inactivation voltage is shifted towards more negative potentials. zERG channel activation is delayed and channel deactivation is accelerated significantly. However, time course of zERG conducted current under action potential clamp is highly similar to the human orthologue. In summary, we show that ERG channels in zebrafish exhibit biophysical properties similar to the human orthologue. Considering the conserved channel function, the zebrafish represents a valuable model to investigate human ERG channel related diseases.

Selective noradrenaline reuptake inhibitor atomoxetine directly blocks hERG currents.

BACKGROUND AND PURPOSE: Atomoxetine is a selective noradrenaline reuptake inhibitor, recently approved for the treatment of attention-deficit/hyperactivity disorder. So far, atomoxetine has been shown to be well tolerated, and cardiovascular effects were found to be negligible. However, two independent cases of QT interval prolongation, associated with atomoxetine overdose, have been reported recently. We therefore analysed acute and subacute effects of atomoxetine on cloned human Ether-à-Go-Go-Related Gene (hERG) channels. EXPERIMENTAL APPROACH: hERG channels were heterologously expressed in Xenopus oocytes and in a human embryonic kidney cell line and hERG currents were measured using voltage clamp and patch clamp techniques. Action potential recordings were made in isolated guinea-pig cardiomyocytes. Gene expression and channel surface expression were analysed using quantitative reverse transcriptase polymerase chain reaction, Western blot and the patch clamp techniques. KEY RESULTS: In human embryonic kidney cells, atomoxetine inhibited hERG current with an IC(50) of 6.3 micromol.L(-1). Development of block and washout were fast. Channel activation and inactivation were not affected. Inhibition was state-dependent, suggesting an open channel block. No use-dependence was observed. Inhibitory effects of atomoxetine were attenuated in the pore mutants Y652A and F656A. In guinea-pig cardiomyocytes, atomoxetine lengthened action potential duration without inducing action potential triangulation. Overnight incubation with high atomoxetine concentrations resulted in a decrease of channel surface expression. CONCLUSIONS AND IMPLICATIONS: Whereas subacute effects of atomoxetine seem negligible under therapeutically relevant concentrations, hERG channel block should be considered in cases of atomoxetine overdose and when administering atomoxetine to patients at increased risk for the development of acquired long-QT syndrome.

Inhibition of cardiac hERG potassium channels by tetracyclic antidepressant mianserin.

The antidepressant mianserin exhibits a tetracyclic structure that is different from typical tricyclic antidepressants (TCA) and that of selective serotonin reuptake inhibitors. In comparison to the older TCA, mianserin has been shown to have a superior risk profile regarding proarrhythmic effects, both in vitro and in vivo. However, the underlying molecular electrophysiological basis has not been elucidated to date. Therefore, we studied the effects of mianserin on cardiac hERG potassium channels, the predominant target of drug-induced proarrhythmia. HERG channels were expressed in the Xenopus oocyte expression system and in human embryonic kidney (HEK) cells and currents were measured with two-microelectrode voltage-clamp and whole-cell patch-clamp, respectively. Mianserin inhibited hERG currents in a dose-dependent manner with an IC(50) of 3.2 micromol/l in HEK cells. Onset of blockade was slow and the inhibitory effect was not reversible upon wash-out of the drug. In hERG channel mutants, Y652A and F656A, lacking aromatic residues in the S6 domain, the effect of mianserin was significantly reduced in comparison to the wild type. Mianserin inhibited hERG currents in the open and inactivated state, but not in the closed states. HERG inactivation kinetics were significantly altered by mianserin without marked effects on channel activation kinetics. The inhibitory effect was not frequency dependent. In conclusion, mianserin is a low-affinity hERG-blocking agent. However, taken together with the lack of APD-prolongation shown in other studies, mianserin seems to have a good safety profile. Lack of consistent QT prolonging effects of mianserin in previous studies may therefore be linked to additional effects such as inhibition of other cardiac ion channels. However, as demonstrated by clinical case reports, mianserin can induce proarrhythmic effects in susceptible patients. Therefore, in patients with complex co-medication (i.e., additional hERG-blocking agents) and in patients with risk factors for acquired long QT syndrome as well as in cases of overdose, adequate monitoring should be recommended.

Deficient zebrafish ether-à-go-go-related gene channel gating causes short-QT syndrome in zebrafish reggae mutants.

BACKGROUND: Genetic predisposition is believed to be responsible for most clinically significant arrhythmias; however, suitable genetic animal models to study disease mechanisms and evaluate new treatment strategies are largely lacking. METHODS AND RESULTS: In search of suitable arrhythmia models, we isolated the zebrafish mutation reggae (reg), which displays clinical features of the malignant human short-QT syndrome such as accelerated cardiac repolarization accompanied by cardiac fibrillation. By positional cloning, we identified the reg mutation that resides within the voltage sensor of the zebrafish ether-à-go-go-related gene (zERG) potassium channel. The mutation causes premature zERG channel activation and defective inactivation, which results in shortened action potential duration and accelerated cardiac repolarization. Genetic and pharmacological inhibition of zERG rescues recessive reg mutant embryos, which confirms the gain-of-function effect of the reg mutation on zERG channel function in vivo. Accordingly, QT intervals in ECGs from heterozygous and homozygous reg mutant adult zebrafish are considerably shorter than in wild-type zebrafish. CONCLUSIONS: With its molecular and pathophysiological concordance to the human arrhythmia syndrome, zebrafish reg represents the first animal model for human short-QT syndrome.

Doxazosin induces apoptosis of cells expressing hERG K+ channels.

The antihypertensive drug doxazosin has been associated with an increased risk for congestive heart failure and cardiomyocyte apoptosis. Human ether-a-go-go-related gene (hERG) K(+) channels, previously shown to be blocked by doxazosin at therapeutically relevant concentrations, represent plasma membrane receptors for the antihypertensive drug. To elucidate the molecular basis for doxazosin-associated pro-apoptotic effects, cell death was studied in human embryonic kidney cells using three independent apoptosis assays. Doxazosin specifically induced apoptosis in hERG-expressing HEK cells, while untransfected control groups were insensitive to treatment with the antihypertensive agent. An unexpected biological mechanism has emerged: binding of doxazosin to its novel membrane receptor, hERG, triggers apoptosis, possibly representing a broader pathophysiological mechanism in drug-induced heart failure.

Kir2.x inward rectifier potassium channels are differentially regulated by adrenergic alpha1A receptors.

Inhibition of I(K1) currents by adrenergic alpha(1) receptors has been observed in cardiomyocytes and has been linked to arrhythmogenesis in an animal model. Both PKC-dependent and PKC-independent pathways have been implied in this regulation. The underlying molecular mechanisms, however, have not been elucidated to date. The molecular basis of native I(K1) current is mainly formed by Kir2.1 (KCNJ2), Kir2.2 (KCNJ12) and Kir2.3 (KCNJ4) channels that are differentially regulated by protein kinases. We therefore sought to investigate the role of those different Kir2.x channel subunits in this regulation and to identify the major signalling pathways involved. Adrenergic alpha(1A) receptors (the predominant cardiac isoform) were co-expressed with cloned Kir2.1, Kir2.2 and Kir2.3 channels in Xenopus oocytes and electrophysiological experiments were performed using two-microelectrode voltage clamp. Native I(K1) currents were measured with the whole-cell patch clamp technique in isolated rat ventricular cardiomyocytes. Activation of co-expressed adrenergic alpha(1A) receptors by phenylephrine induced differential effects in Kir2.x channels. No effect was noticed in Kir2.1 channels. However, a marked inhibitory effect was observed in Kir2.2 channels. This regulation was not attenuated by inhibitors of PKC, CamKII and PKA (chelerythrine, KN-93, KT-5720), and mutated Kir2.2 channels lacking functional phosphorylation sites for PKC and PKA exhibited the same effect as Kir2.2 wild-type channels. By contrast, the regulation could be suppressed by the general tyrosine kinase inhibitor genistein and by the src tyrosine kinase inhibitor PP2 indicating an essential role of src kinases. This finding was validated in rat ventricular cardiomyocytes where co-application of PP2 strongly attenuated the inhibitory regulation of I(K1) current by adrenergic alpha(1) receptors. The inactive analogue PP3 was tested as negative control for PP2 and did not reproduce the effects of PP2. In Kir2.3 channels, a marked inhibitory effect of alpha(1A) receptor activation was observed. This regulation could be attenuated by inhibition of PKC with chelerythrine or with Ro-32-0432, but not by tyrosine kinase inhibition with genistein. In summary, on the molecular level the inhibitory regulation of I(K1) currents by adrenergic alpha(1A) receptors is probably based on effects on Kir2.2 and Kir2.3 channels. Kir2.2 is regulated via src tyrosine kinase pathways independent of protein kinase C, whereas Kir2.3 is inhibited by protein kinase C-dependent pathways. Src tyrosine kinase pathways are essential for the inhibition of native I(K1) current by adrenergic alpha(1) receptors. This regulation may contribute to arrhythmogenesis under adrenergic stimulation.

Green tea flavonoid epigallocatechin-3-gallate (EGCG) inhibits cardiac hERG potassium channels.

The catechin EGCG is the main flavonoid compound of green tea and has received enormous pharmacological attention because of its putative beneficial health effects. This study investigated for the first time the effect of EGCG on hERG channels, the main pharmacological target of drugs that cause acquired long QT syndrome. Cloned hERG channels were expressed in Xenopus oocytes and in HEK293 cells. Heterologous hERG currents were inhibited by EGCG with an IC50 of 6.0 micromol/l in HEK293 cells and an IC50 of 20.5 micromol/l in Xenopus laevis oocytes. Onset of effect was slow and only little recovery from inhibition was observed upon washout. In X. laevis oocytes EGCG inhibited hERG channels in the open and inactivated states, but not in the closed states. The half-maximal activation voltage of hERG currents was shifted by EGCG towards more positive potentials. In conclusion, EGCG is a low-affinity inhibitor of hERG sharing major electrophysiological features with pharmaceutical hERG antagonists.

Anticholinergic antiparkinson drug orphenadrine inhibits HERG channels: block attenuation by mutations of the pore residues Y652 or F656.

The anticholinergic antiparkinson drug orphenadrine is an antagonist at central and peripheral muscarinic receptors. Orphenadrine intake has recently been linked to QT prolongation and Torsade-de-Pointes tachycardia. So far, inhibitory effects on I (Kr) or cloned HERG channels have not been examined. HERG channels were heterologously expressed in a HEK 293 cell line and in Xenopus oocytes and HERG current was measured using the whole cell patch clamp and the double electrode voltage clamp technique. Orphenadrine inhibits cloned HERG channels in a concentration dependent manner, yielding an IC(50) of 0.85 microM in HEK cells. Onset of block is fast and reversible upon washout. Orphenadrine does not alter the half-maximal activation voltage of HERG channels. There is no shift of the half-maximal steady-state-inactivation voltage. Time constants of direct channel inactivation are not altered significantly and there is no use-dependence of block. HERG blockade is attenuated significantly in mutant channels lacking either of the aromatic pore residues Y652 and F656. In conclusion, we show that the anticholinergic agent orphenadrine is an antagonist at HERG channels. These results provide a novel molecular basis for the reported proarrhythmic side effects of orphenadrine.

Activation of inwardly rectifying Kir2.x potassium channels by beta 3-adrenoceptors is mediated via different signaling pathways with a predominant role of PKC for Kir2.1 and of PKA for Kir2.2.

beta(3)-adrenoceptors have recently been shown to induce a complex modulation of intracellular signaling pathways including cyclic guanine monophosphate, cyclic adenosine monophosphate, nitric oxide, and protein kinases A and C. They are expressed in a broad variety of tissues including the myocardium, vascular smooth muscle, and endothelium. In those tissues, resting membrane potential is controlled mainly by inwardly rectifying potassium channels of the Kir2 family namely, Kir2.1 in the vascular smooth muscle, Kir2.1-2.3 in the myocardium, and Kir2.1-2.2 in the endothelium. In the present study, we investigated the possible modulation of Kir2 channel function by beta(3)-adrenoceptors in an expression system. Human-cloned beta(3)-adrenoceptors and Kir2.1 (KCNJ2), Kir2.2 (KCNJ12), and Kir2.3 (KCNJ4) channels were coexpressed in Xenopus oocytes, and currents were measured with double-microelectrode voltage clamp. Activation of beta(3)-adrenoceptors with isoproterenol resulted in markedly increased currents in Kir2.1 and in Kir2.2 potassium channels with EC50 values of 27 and 18 nM, respectively. In contrast, Kir2.3 currents were not modulated. Coapplication of specific inhibitors of protein kinase A (KT-5720) and calmodulin kinase II (KN-93) had no effects on the observed regulation in Kir2.1. However, coapplication of protein kinase C (PKC) inhibitors staurosporine and chelerythrine suppressed the observed effect. In Kir2.2, coapplication of KT-5720 reduced the effect of beta(3)-adrenoceptor activation. No differences in current increase after application of isoproterenol were observed between mutant Kir2.2 potassium channels lacking all functional PKC phosphorylation sites and Kir2.2 wild-type channels. In heteromeric Kir2.x channels, all types of heteromers were activated. The effect was most pronounced in Kir2.1/Kir2.2 and in Kir2.2/Kir2.3 channels. In summary, homomeric and heteromeric Kir2.x channels are activated by beta(3)-adrenoceptors via different protein kinase-dependent pathways: Kir2.1 subunits are modulated by PKC, whereas Kir2.2 is modulated by protein kinase A. In heteromeric composition, a marked activation of currents can be observed particularly with involvement of Kir2.2 subunits. This regulation may contribute to the hyperpolarizing effects of beta(3)-adrenoceptors in tissues that exhibit modulation by Kir2 channel function.

Atrial septal aneurysm mimicking ECG signs of enlarged right atrium.

In a routine ECG from a young asymptomatic woman, changes in P-wave morphology and the frontal plane atrial vector were noted. Two-dimensional echocardiography revealed a large atrial septal aneurysm as probable underlying cause. This case report demonstrates that non-specific right atrial ECG signs may be indicative of lone atrial septal aneurysm.

Orange flavonoid hesperetin modulates cardiac hERG potassium channel via binding to amino acid F656.

BACKGROUND AND AIMS: Hesperetin belongs to the flavonoid subgroup classified as citrus flavonoids and is the main flavonoid in oranges. A high dietary intake of flavonoids has been associated with a significant reduction in cardiovascular mortality. HERG potassium channels play a major role in cardiac repolarisation and represent the most important pharmacologic target of both antiarrhythmic and proarrhythmic drugs. METHODS AND RESULTS: We used the two-microelectrode voltage-clamp technique to analyse inhibitory effects of hesperetin on hERG potassium channels heterologously expressed in Xenopus oocytes. Hesperetin blocked hERG potassium channels in a concentration dependent manner. Onset of block was fast and completely reversible upon wash-out. There was no significant effect of hesperetin on channel kinetics. Affinity of hesperetin to mutant F656A hERG channel was significantly decreased compared to WT hERG, indicating a binding site in the channel pore cavity. In contrast, affinity of hesperetin to Y652A hERG was not different from the affinity to WT hERG. CONCLUSION: We found an antagonist of cardiac hERG channels that modulates hERG currents by accessing the aromatic pore binding site, particularly amino acid phe-656. Regarding high hesperetin concentrations found in oranges and the increasing consumption of oranges and orange juice in Europe, potential effects of hesperetin on cardiac electrophysiology in vivo deserve further investigation.