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1.
Internist (Berl) ; 62(11): 1180-1190, 2021 Nov.
Article in German | MEDLINE | ID: mdl-34648044

ABSTRACT

Digital health solutions, applications of artificial intelligence (AI) and new technologies, such as cardiac magnetic resonance imaging and cardiac human genetics are currently being validated in cardiac healthcare pathways. They show promising approaches for improving existing healthcare structures in the future by strengthening the focus on predictive, preventive and personalized medicine. In addition, the accompanying use of digital health applications will become increasingly more important in the future healthcare, especially in patients with chronic diseases. In this article, the authors describe a case of chronic heart failure (HF) as an example to provide an overview of how digitalized healthcare can be efficiently designed across sectors and disciplines in the future. Moreover, the importance of a self-determined patient management for the treatment process itself is underlined. Since HF is frequently accompanied by various comorbidities during the course of the disease that are often recognized only after a delay, the necessity for a timely simultaneous and preventive treatment of multiple comorbidities in cardiovascular diseases is emphasized. Against this background the currently separately applied disease management programs (DMP) are critically questioned. The development of a holistic DMP encompassing all indications for the treatment of chronic diseases may pave the way to a more efficient medical care system.


Subject(s)
Artificial Intelligence , Heart Failure , Delivery of Health Care , Forecasting , Heart , Heart Failure/diagnosis , Heart Failure/therapy , Humans
2.
Herzschrittmacherther Elektrophysiol ; 32(2): 227-235, 2021 Jun.
Article in German | MEDLINE | ID: mdl-33982176

ABSTRACT

The possibility of outpatient implantation of defibrillators, devices for cardiac resynchronization, and event recorders (collectively called cardiac implantable electronic devices, CIEDs) is becoming increasingly important. In Germany, only a few options for outpatient implantation are currently realized. Furthermore, there is a lack of uniform, recognized, and binding quality criteria. This article provides insight into the current contract constellations for outpatient surgery and defines a first, holistic quality concept for outpatient implantations of CIEDs. The present works aims to initiate a discourse in the specialist society in order to define a coordinated, binding quality concept. Then, this should serve as the basis for future outpatient implantation services, enabling comparability and to contribute long-term evidence.


Subject(s)
Cardiac Resynchronization Therapy , Defibrillators, Implantable , Pacemaker, Artificial , Cardiac Resynchronization Therapy Devices , Germany , Humans , Outpatients
4.
Naunyn Schmiedebergs Arch Pharmacol ; 390(5): 493-503, 2017 May.
Article in English | MEDLINE | ID: mdl-28331977

ABSTRACT

The cardiac IK1 current stabilizes the resting membrane potential of cardiomyocytes. Protein kinase A (PKA) induces an inhibition of IK1 current which strongly promotes focal arrhythmogenesis. The molecular mechanisms underlying this regulation have only partially been elucidated yet. Furthermore, the role of A-kinase anchoring proteins (AKAPs) in this regulation has not been examined to date. The objective of this project was to elucidate the molecular mechanisms underlying the inhibition of IK1 by PKA and to identify novel molecular targets for antiarrhythmic therapy downstream ß-adrenoreceptors. Patch clamp and voltage clamp experiments were used to record currents and co-immunoprecipitation, and co-localization experiments were performed to show spatial and functional coupling. Activation of PKA inhibited IK1 current in rat cardiomyocytes. This regulation was markedly attenuated by disrupting PKA-binding to AKAPs with the peptide inhibitor AKAP-IS. We observed functional and spatial coupling of the plasma membrane-associated AKAP15 and AKAP79 to Kir2.1 and Kir2.2 channel subunits, but not to Kir2.3 channels. In contrast, AKAPyotiao had no functional effect on the PKA regulation of Kir channels. AKAP15 and AKAP79 co-immunoprecipitated with and co-localized to Kir2.1 and Kir2.2 channel subunits in ventricular cardiomyocytes. In this study, we provide evidence for coupling of cardiac Kir2.1 and Kir2.2 subunits with the plasma membrane-bound AKAPs 15 and 79. Cardiac membrane-associated AKAPs are a functionally essential part of the regulatory cascade determining IK1 current function and may be novel molecular targets for antiarrhythmic therapy downstream from ß-adrenoreceptors.


Subject(s)
A Kinase Anchor Proteins/metabolism , Cell Membrane/enzymology , Cyclic AMP-Dependent Protein Kinases/metabolism , Myocytes, Cardiac/enzymology , Potassium Channels, Inwardly Rectifying/metabolism , A Kinase Anchor Proteins/antagonists & inhibitors , A Kinase Anchor Proteins/genetics , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/metabolism , Animals , CHO Cells , Cell Membrane/drug effects , Cricetulus , Enzyme Activation , Enzyme Activators/pharmacology , HEK293 Cells , Humans , Immunoprecipitation , Ion Channel Gating , Membrane Potentials , Microinjections , Myocytes, Cardiac/drug effects , Patch-Clamp Techniques , Peptides/pharmacology , Potassium Channels, Inwardly Rectifying/genetics , Protein Binding , Rats , Transfection , Xenopus
5.
J Biol Methods ; 4(3): e78, 2017.
Article in English | MEDLINE | ID: mdl-31453232

ABSTRACT

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.

6.
Herzschrittmacherther Elektrophysiol ; 27(3): 295-306, 2016 Sep.
Article in German | MEDLINE | ID: mdl-27576696

ABSTRACT

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.


Subject(s)
Anticoagulants/administration & dosage , Atrial Fibrillation/drug therapy , Cardiology/standards , Practice Guidelines as Topic , Stroke/prevention & control , Administration, Oral , Atrial Fibrillation/complications , Evidence-Based Medicine/standards , Germany , Heart Valve Diseases/complications , Heart Valve Diseases/drug therapy , Stroke/etiology , Treatment Outcome
7.
PLoS One ; 11(5): e0156181, 2016.
Article in English | MEDLINE | ID: mdl-27214373

ABSTRACT

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.


Subject(s)
Membrane Potentials/drug effects , Myocytes, Cardiac/physiology , Potassium Channels, Inwardly Rectifying/physiology , Protein Kinase C/physiology , Animals , Cells, Cultured , Down-Regulation/drug effects , Female , Membrane Potentials/physiology , Mice , Myocytes, Cardiac/drug effects , Patch-Clamp Techniques , Potassium Channels, Inwardly Rectifying/drug effects , Protein Kinase C/metabolism , Protein Kinase Inhibitors/pharmacology , Rats , Xenopus laevis
8.
EPMA J ; 5(1): 15, 2014.
Article in English | MEDLINE | ID: mdl-25243024

ABSTRACT

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'.

9.
Biochem Biophys Res Commun ; 424(2): 315-20, 2012 Jul 27.
Article in English | MEDLINE | ID: mdl-22749993

ABSTRACT

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.


Subject(s)
Adrenergic beta-3 Receptor Antagonists/pharmacology , Potassium Channels, Inwardly Rectifying/antagonists & inhibitors , Propanolamines/pharmacology , Receptors, Adrenergic, beta-3/metabolism , Animals , Oocytes , Xenopus laevis
10.
Biochem Biophys Res Commun ; 408(2): 218-24, 2011 May 06.
Article in English | MEDLINE | ID: mdl-21458413

ABSTRACT

Inherited cardiac arrhythmias are caused by genetic defects in ion channels and associated proteins. Mutations in these channels often do not affect their biophysical properties, but rather interfere with their trafficking to the cell membrane. Accordingly, strategies that could reroute the mutated channels to the membrane should be sufficient to restore the electrical properties of the affected cells, thereby suppressing the underlying arrhythmia. We identified here both, embryonic and adult zebrafish breakdance (bre) as a valuable model for human Long-QT syndrome. Electrocardiograms of adult homozygous bre mutants exhibit significant QT prolongation caused by delayed repolarization of the ventricle. We further show that the bre mutation (zERG(I59S)) disrupts ERG protein trafficking, thereby reducing the amount of active potassium channels on the cell membrane. Interestingly, improvement of channel trafficking by cisapride or dimethylsulfoxid is sufficient to reconstitute ERG channels on the cell membrane in a manner that suffices to suppress the Long-QT induced arrhythmia in breakdance mutant zebrafish. In summary, we show for the first time that therapeutic intervention can cure protein trafficking defects and the associated cardiac arrhythmia in vivo.


Subject(s)
Ether-A-Go-Go Potassium Channels/metabolism , Long QT Syndrome/metabolism , Zebrafish Proteins/metabolism , Animals , Disease Models, Animal , Ether-A-Go-Go Potassium Channels/genetics , HEK293 Cells , Heart Rate/genetics , Humans , Long QT Syndrome/genetics , Long QT Syndrome/physiopathology , Mutation , Protein Transport/genetics , Ventricular Dysfunction/genetics , Ventricular Dysfunction/physiopathology , Zebrafish , Zebrafish Proteins/genetics
11.
Cardiovasc Ther ; 28(4): e46-52, 2010 Aug.
Article in English | MEDLINE | ID: mdl-20633021

ABSTRACT

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.


Subject(s)
Cardiovascular Agents/pharmacology , Cardiovascular Diseases/prevention & control , Cardiovascular System/drug effects , Dietary Supplements , Flavonoids/pharmacology , Ion Channels/drug effects , Animals , Cardiovascular Diseases/metabolism , Cardiovascular Diseases/physiopathology , Cardiovascular System/metabolism , Cardiovascular System/physiopathology , Humans , Ion Channels/metabolism , Ion Transport , Membrane Potentials
12.
Naunyn Schmiedebergs Arch Pharmacol ; 381(5): 385-400, 2010 May.
Article in English | MEDLINE | ID: mdl-20229012

ABSTRACT

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.


Subject(s)
Amoxapine/toxicity , Antidepressive Agents, Second-Generation/toxicity , Apoptosis/drug effects , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Amoxapine/administration & dosage , Animals , Antidepressive Agents, Second-Generation/administration & dosage , Cell Line , Ether-A-Go-Go Potassium Channels/metabolism , Humans , Inhibitory Concentration 50 , Oocytes , Patch-Clamp Techniques , Protein Binding , Protein Transport/drug effects , Xenopus laevis
13.
Naunyn Schmiedebergs Arch Pharmacol ; 381(3): 261-70, 2010 Mar.
Article in English | MEDLINE | ID: mdl-19777211

ABSTRACT

Two-pore-domain (K(2P)) potassium channels mediate background potassium currents, stabilizing resting membrane potential and expediting action potential repolarization. In the heart, K(2P)3.1 (TASK-1) channels are implicated in the cardiac plateau current, I ( KP ). Class III antiarrhythmic drugs target cardiac K(+) currents, resulting in action potential prolongation and suppression of atrial and ventricular arrhythmias. The objective of this study was to investigate acute effects of the class III antiarrhythmic drug amiodarone on human K(2P)3.1 channels. Potassium currents were recorded from Xenopus oocytes using the two-microelectrode voltage clamp technique. Amiodarone produced concentration-dependent inhibition of hK(2P)3.1 currents (IC(50) = 0.40 microM) with maximum current reduction of 58.1%. Open rectification properties that are characteristic to hK(2P)3.1 currents were not altered by amiodarone. Channels were blocked in open and closed states in reverse frequency-dependent manner. hK(2P)3.1 channel inhibition was voltage-independent at voltages between -40 and +60 mV. Modulation of protein kinase C activity by amiodarone does not contribute to hK(2P)3.1 current reduction, as pre-treatment with the protein kinase C inhibitor, staurosporine, did not affect amiodarone block. Amiodarone is an inhibitor of cardiac hK(2P)3.1 background channels. Amiodarone blockade of hK(2P)3.1 may cause prolongation of cardiac repolarization and action potential duration in patients with high individual plasma concentrations, possibly contributing to the antiarrhythmic efficacy of the class III drug.


Subject(s)
Amiodarone/pharmacology , Anti-Arrhythmia Agents/pharmacology , Myocardium/metabolism , Nerve Tissue Proteins/antagonists & inhibitors , Potassium Channels, Tandem Pore Domain/antagonists & inhibitors , Action Potentials/drug effects , Animals , Cloning, Molecular , Dose-Response Relationship, Drug , Female , Oocytes/cytology , Oocytes/metabolism , Patch-Clamp Techniques , Protein Kinase C/antagonists & inhibitors , Protein Kinase C/metabolism , Staurosporine/pharmacology , Xenopus laevis
14.
J Mol Cell Cardiol ; 48(1): 230-7, 2010 Jan.
Article in English | MEDLINE | ID: mdl-19540844

ABSTRACT

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.


Subject(s)
KCNQ1 Potassium Channel/metabolism , Romano-Ward Syndrome/genetics , Adult , DNA Mutational Analysis , Electrophysiology , Female , Genetic Predisposition to Disease , Humans , KCNQ1 Potassium Channel/genetics , Male , Mutation , Pedigree , Potassium Channels, Voltage-Gated/genetics
15.
Biochem Biophys Res Commun ; 381(2): 159-64, 2009 Apr 03.
Article in English | MEDLINE | ID: mdl-19232322

ABSTRACT

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.


Subject(s)
Ether-A-Go-Go Potassium Channels/physiology , Zebrafish Proteins/physiology , Zebrafish/physiology , Animals , Ether-A-Go-Go Potassium Channels/agonists , Ether-A-Go-Go Potassium Channels/genetics , Humans , Membrane Potentials , Oocytes , Xenopus , Zebrafish/genetics , Zebrafish Proteins/agonists , Zebrafish Proteins/genetics
16.
Br J Pharmacol ; 156(2): 226-36, 2009 Jan.
Article in English | MEDLINE | ID: mdl-19154426

ABSTRACT

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.


Subject(s)
Adrenergic Uptake Inhibitors/adverse effects , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Propylamines/adverse effects , Action Potentials/drug effects , Adrenergic Uptake Inhibitors/pharmacology , Animals , Atomoxetine Hydrochloride , Blotting, Western , Cell Line , Cloning, Molecular , Dose-Response Relationship, Drug , Ether-A-Go-Go Potassium Channels/metabolism , Guinea Pigs , Humans , In Vitro Techniques , Myocytes, Cardiac/drug effects , Myocytes, Cardiac/physiology , Oocytes/drug effects , Oocytes/physiology , Patch-Clamp Techniques , Propylamines/pharmacology , Reverse Transcriptase Polymerase Chain Reaction , Xenopus
17.
Biochem Biophys Res Commun ; 377(3): 981-6, 2008 Dec 19.
Article in English | MEDLINE | ID: mdl-18976636

ABSTRACT

The renal inward rectifier potassium channel Kir7.1 has been proposed to be functionally important for tubular K(+) recycling and secretion. This study investigated the regulation of Kir7.1 by PKA and PKC. Cloned human Kir7.1 channels were expressed heterologously in Xenopus oocytes. After pharmacological PKC activation, Kir7.1 currents were strongly inhibited. Co-application of PKC inhibitors attenuated this effect. Inactivation of PKC consensus sites also strongly attenuated the effect with a single site ((201)S) being essential for almost the total PKC sensitivity. In contrast, PKA activation induced an increase of Kir7.1 currents. This effect was absent in mutant Kir7.1 channels lacking PKA consensus site (287)S. In summary, this study demonstrates the dual regulation of Kir7.1 channel function by PKA and PKC. Structurally, these regulations depend on two key residues in the C-terminal channel domain ((Ser)201 for PKC and (Ser)287 for PKA).


Subject(s)
Cyclic AMP-Dependent Protein Kinases/metabolism , Kidney/metabolism , Potassium Channels, Inwardly Rectifying/metabolism , Protein Kinase C/metabolism , Animals , Cloning, Molecular , Enzyme Activation , Humans , Kidney/enzymology , Molecular Sequence Data , Oocytes , Phosphorylation , Potassium Channels, Inwardly Rectifying/antagonists & inhibitors , Potassium Channels, Inwardly Rectifying/genetics , Protein Structure, Tertiary , Serine/genetics , Serine/metabolism , Transfection , Xenopus
18.
Naunyn Schmiedebergs Arch Pharmacol ; 378(1): 73-83, 2008 Jul.
Article in English | MEDLINE | ID: mdl-18458880

ABSTRACT

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.


Subject(s)
Antidepressive Agents, Second-Generation/toxicity , Ether-A-Go-Go Potassium Channels/antagonists & inhibitors , Mianserin/toxicity , Animals , Antidepressive Agents, Second-Generation/administration & dosage , Cell Line , Dose-Response Relationship, Drug , Electrophysiology , Female , Humans , Inhibitory Concentration 50 , Kidney/cytology , Mianserin/administration & dosage , Oocytes/drug effects , Patch-Clamp Techniques/methods , Toxicity Tests , Xenopus
19.
Circulation ; 117(7): 866-75, 2008 Feb 19.
Article in English | MEDLINE | ID: mdl-18250272

ABSTRACT

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.


Subject(s)
Arrhythmias, Cardiac/genetics , Disease Models, Animal , Ether-A-Go-Go Potassium Channels/physiology , Zebrafish Proteins/physiology , Zebrafish/genetics , Action Potentials/genetics , Amino Acid Substitution , Animals , Arrhythmias, Cardiac/drug therapy , Arrhythmias, Cardiac/embryology , Arrhythmias, Cardiac/physiopathology , Atrial Fibrillation/drug therapy , Atrial Fibrillation/genetics , Atrial Fibrillation/physiopathology , Ether-A-Go-Go Potassium Channels/deficiency , Ether-A-Go-Go Potassium Channels/genetics , Genotype , Heart/embryology , Ion Channel Gating/genetics , Mutation, Missense , Myocardial Contraction , Oocytes , Patch-Clamp Techniques , Potassium/metabolism , Recombinant Fusion Proteins/physiology , Sinoatrial Block/drug therapy , Sinoatrial Block/genetics , Sinoatrial Block/physiopathology , Syndrome , Terfenadine/therapeutic use , Xenopus laevis , Zebrafish/embryology , Zebrafish/physiology , Zebrafish Proteins/deficiency , Zebrafish Proteins/genetics
20.
Eur J Pharmacol ; 579(1-3): 98-103, 2008 Jan 28.
Article in English | MEDLINE | ID: mdl-18054910

ABSTRACT

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.


Subject(s)
Antihypertensive Agents/pharmacology , Apoptosis/drug effects , Doxazosin/pharmacology , Ether-A-Go-Go Potassium Channels/drug effects , Adrenergic alpha-Antagonists/pharmacology , Cell Line , Electrophysiology , Ether-A-Go-Go Potassium Channels/metabolism , Flow Cytometry , Humans , In Situ Nick-End Labeling , Staining and Labeling
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