Acute antiarrhythmic effects of SGLT2 inhibitors-dapagliflozin lowers the excitability of atrial cardiomyocytes.

In recent years, SGLT2 inhibitors have become an integral part of heart failure therapy, and several mechanisms contributing to cardiorenal protection have been identified. In this study, we place special emphasis on the atria and investigate acute electrophysiological effects of dapagliflozin to assess the antiarrhythmic potential of SGLT2 inhibitors. Direct electrophysiological effects of dapagliflozin were investigated in patch clamp experiments on isolated atrial cardiomyocytes. Acute treatment with elevated-dose dapagliflozin caused a significant reduction of the action potential inducibility, the amplitude and maximum upstroke velocity. The inhibitory effects were reproduced in human induced pluripotent stem cell-derived cardiomyocytes, and were more pronounced in atrial compared to ventricular cells. Hypothesizing that dapagliflozin directly affects the depolarization phase of atrial action potentials, we examined fast inward sodium currents in human atrial cardiomyocytes and found a significant decrease of peak sodium current densities by dapagliflozin, accompanied by a moderate inhibition of the transient outward potassium current. Translating these findings into a porcine large animal model, acute elevated-dose dapagliflozin treatment caused an atrial-dominant reduction of myocardial conduction velocity in vivo. This could be utilized for both, acute cardioversion of paroxysmal atrial fibrillation episodes and rhythm control of persistent atrial fibrillation. In this study, we show that dapagliflozin alters the excitability of atrial cardiomyocytes by direct inhibition of peak sodium currents. In vivo, dapagliflozin exerts antiarrhythmic effects, revealing a potential new additional role of SGLT2 inhibitors in the treatment of atrial arrhythmias.

Activation of neurokinin-III receptors modulates human atrial TASK-1 currents.

RATIONALE: The neurokinin-III receptor was recently shown to regulate atrial cardiomyocyte excitability by inhibiting atrial background potassium currents. TASK-1 (hK2P3.1) two-pore-domain potassium channels, which are expressed atrial-specifically in the human heart, contribute significantly to atrial background potassium currents. As TASK-1 channels are regulated by a variety of intracellular signalling cascades, they represent a promising candidate for mediating the electrophysiological effects of the Gq-coupled neurokinin-III receptor. OBJECTIVE: To investigate whether TASK-1 channels mediate the neurokinin-III receptor activation induced effects on atrial electrophysiology. METHODS AND RESULTS: In Xenopus laevis oocytes, heterologously expressing neurokinin-III receptor and TASK-1, administration of the endogenous neurokinin-III receptor ligands substance P or neurokinin B resulted in a strong TASK-1 current inhibition. This could be reproduced by application of the high affinity neurokinin-III receptor agonist senktide. Moreover, preincubation with the neurokinin-III receptor antagonist osanetant blunted the effect of senktide. Mutagenesis studies employing TASK-1 channel constructs which lack either protein kinase C (PKC) phosphorylation sites or the domain which is regulating the diacyl glycerol (DAG) sensitivity domain of TASK-1 revealed a protein kinase C independent mechanism of TASK-1 current inhibition: upon neurokinin-III receptor activation TASK-1 channels are blocked in a DAG-dependent fashion. Finally, effects of senktide on atrial TASK-1 currents could be reproduced in patch-clamp measurements, performed on isolated human atrial cardiomyocytes. CONCLUSIONS: Heterologously expressed human TASK-1 channels are inhibited by neurokinin-III receptor activation in a DAG dependent fashion. Patch-clamp measurements, performed on human atrial cardiomyocytes suggest that the atrial-specific effects of neurokinin-III receptor activation on cardiac excitability are predominantly mediated via TASK-1 currents.

Electrophysiological effects of non-vitamin K antagonist oral anticoagulants on atrial repolarizing potassium channels.

AIMS: Non-vitamin K antagonist oral anticoagulants (NOACs) are widely used in the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation (AF). The efficacy of NOACs has been attributed in part to pleiotropic effects that are mediated through effects on thrombin, factor Xa, and their respective receptors. Direct pharmacological effects of NOACs and cardiac ion channels have not been addressed to date. We hypothesized that the favourable clinical outcome of NOAC use may be associated with previously unrecognized effects on atrial repolarizing potassium channels. METHODS AND RESULTS: This study was designed to elucidate acute pharmacological effects of NOACs on cloned ion channels Kv11.1, Kv1.5, Kv4.3, Kir2.1, Kir2.2, and K2P2.1 contributing to IKr, IKur, Ito, IK1, and IK2P K+ currents. Human genes, KCNH2, KCNA5, KCND3, KCNJ2, KCNJ12, and KCNK2, were heterologously expressed in Xenopus laevis oocytes, and currents were recorded using voltage-clamp electrophysiology. Apixaban, dabigatran, edoxaban, and rivaroxaban applied at 1 µM did not significantly affect peak current amplitudes of Kv11.1, Kv1.5, Kv4.3, Kir2.1, Kir2.2, or K2P2.1 K+ channels. Furthermore, biophysical characterization did not reveal significant effects of NOACs on current-voltage relationships of study channels. CONCLUSION: Apixaban, dabigatran, edoxaban, and rivaroxaban did not exhibit direct functional interactions with human atrial K+ channels underlying IKr, IKur, Ito, IK1, and IK2P currents that could account for beneficial clinical outcome associated with the drugs. Indirect or chronic effects and potential underlying signalling mechanisms remain to be investigated.

Identification of the A293 (AVE1231) Binding Site in the Cardiac Two-Pore-Domain Potassium Channel TASK-1: a Common Low Affinity Antiarrhythmic Drug Binding Site.

BACKGROUND/AIMS: The two-pore-domain potassium channel TASK-1 regulates atrial action potential duration. Due to the atrium-specific expression of TASK-1 in the human heart and the functional upregulation of TASK-1 currents in atrial fibrillation (AF), TASK-1 represents a promising target for the treatment of AF. Therefore, detailed knowledge of the molecular determinants of TASK-1 inhibition may help to identify new drugs for the future therapy of AF. In the current study, the molecular determinants of TASK-1 inhibition by the potent and antiarrhythmic compound A293 (AVE1231) were studied in detail. METHODS: Alanine-scanning mutagenesis together with two-electrode voltage-clamp recordings were combined with in silico docking experiments. RESULTS: Here, we have identified Q126 located in the M2 segment together with L239 and N240 of the M4 segment as amino acids essential for the A293-mediated inhibition of TASK-1. These data indicate a binding site which is different to that of A1899 for which also residues of the pore signature sequence and the late M4 segments are essential. Using in silico docking experiments, we propose a binding site at the lower end of the cytosolic pore, located at the entry to lateral side fenestrations of TASK-1. Strikingly, TASK-1 inhibition by the low affinity antiarrhythmic TASK-1 blockers propafenone, amiodarone and carvedilol was also strongly diminished by mutations at this novel binding site. CONCLUSION: We have identified the A293 binding site in the central cavity of TASK-1 and propose that this site might represent a conserved site of action for many low affinity antiarrhythmic TASK-1 blockers.

N-Glycosylation of TREK-1/hK2P2.1 Two-Pore-Domain Potassium (K2P) Channels.

Mechanosensitive hTREK-1 two-pore-domain potassium (hK2P2.1) channels give rise to background currents that control cellular excitability. Recently, TREK-1 currents have been linked to the regulation of cardiac rhythm as well as to hypertrophy and fibrosis. Even though the pharmacological and biophysical characteristics of hTREK-1 channels have been widely studied, relatively little is known about their posttranslational modifications. This study aimed to evaluate whether hTREK-1 channels are N-glycosylated and whether glycosylation may affect channel functionality. Following pharmacological inhibition of N-glycosylation, enzymatic digestion or mutagenesis, immunoblots of Xenopus laevis oocytes and HEK-293T cell lysates were used to assess electrophoretic mobility. Two-electrode voltage clamp measurements were employed to study channel function. TREK-1 channel subunits undergo N-glycosylation at asparagine residues 110 and 134. The presence of sugar moieties at these two sites increases channel function. Detection of glycosylation-deficient mutant channels in surface fractions and recordings of macroscopic potassium currents mediated by these subunits demonstrated that nonglycosylated hTREK-1 channel subunits are able to reach the cell surface in general but with seemingly reduced efficiency compared to glycosylated subunits. These findings extend our understanding of the regulation of hTREK-1 currents by posttranslational modifications and provide novel insights into how altered ion channel glycosylation may promote arrhythmogenesis.

Extracellular vesicles mediate intercellular communication: Transfer of functionally active microRNAs by microvesicles into phagocytes.

Cell activation and apoptosis lead to the formation of extracellular vesicles (EVs) such as exosomes or microvesicles (MVs). EVs have been shown to modulate immune responses; recently, MVs were described to carry microRNA (miRNA) and a role for MVs in the pathogenesis of autoimmune diseases has been discussed. Here we systematically characterized MVs and exosomes according to their release stimuli. The miRNA content of viable or apoptotic human T lymphocytes and the corresponding MVs was analyzed. miRNA, protein and surface marker expression, as well as cytokine release by human monocytes was measured after EV engulfment. Finally, miRNA expression in T lymphocytes and MVs of healthy individuals was compared with those of systemic lupus erythematosus (SLE) patients. We demonstrate that, depending on the stimuli, distinct subtypes of EVs are released, differing in size and carrying a specific RNA profile. We observed an accumulation of distinct miRNAs in MVs after induction of apoptosis and the transfer of functional miRNA by MVs into human monocytes. MVs released from apoptotic cells provoke less of an inflammatory response than those released from viable cells. MiR-155*, miR-34b and miR-34a levels in T lymphocytes and corresponding MVs were deregulated in SLE when compared to healthy individuals.

New Targets for Old Drugs: Cardiac Glycosides Inhibit Atrial-Specific K2P3.1 (TASK-1) Channels.

Cardiac glycosides have been used in the treatment of arrhythmias for more than 200 years. Two-pore-domain (K2P) potassium channels regulate cardiac action potential repolarization. Recently, K2P3.1 [tandem of P domains in a weak inward rectifying K+ channel (TWIK)-related acid-sensitive K+ channel (TASK)-1] has been implicated in atrial fibrillation pathophysiology and was suggested as an atrial-selective antiarrhythmic drug target. We hypothesized that blockade of cardiac K2P channels contributes to the mechanism of action of digitoxin and digoxin. All functional human K2P channels were screened for interactions with cardiac glycosides. Human K2P channel subunits were expressed in Xenopus laevis oocytes, and voltage clamp electrophysiology was used to record K+ currents. Digitoxin significantly inhibited K2P3.1 and K2P16.1 channels. By contrast, digoxin displayed isolated inhibitory effects on K2P3.1. K2P3.1 outward currents were reduced by 80% (digitoxin, 1 Hz) and 78% (digoxin, 1 Hz). Digitoxin inhibited K2P3.1 currents with an IC50 value of 7.4 µM. Outward rectification properties of the channel were not affected. Mutagenesis studies revealed that amino acid residues located at the cytoplasmic site of the K2P3.1 channel pore form parts of a molecular binding site for cardiac glycosides. In conclusion, cardiac glycosides target human K2P channels. The antiarrhythmic significance of repolarizing atrial K2P3.1 current block by digoxin and digitoxin requires validation in translational and clinical studies.

Atrial fibrillation and heart failure-associated remodeling of two-pore-domain potassium (K2P) channels in murine disease models: focus on TASK-1.

Understanding molecular mechanisms involved in atrial tissue remodeling and arrhythmogenesis in atrial fibrillation (AF) is essential for developing specific therapeutic approaches. Two-pore-domain potassium (K2P) channels modulate cellular excitability, and TASK-1 (K2P3.1) currents were recently shown to alter atrial action potential duration in AF and heart failure (HF). Finding animal models of AF that closely resemble pathophysiological alterations in human is a challenging task. This study aimed to analyze murine cardiac expression patterns of K2P channels and to assess modulation of K2P channel expression in murine models of AF and HF. Expression of cardiac K2P channels was quantified by real-time qPCR and immunoblot in mouse models of AF [cAMP-response element modulator (CREM)-IbΔC-X transgenic animals] or HF (cardiac dysfunction induced by transverse aortic constriction, TAC). Cloned murine, human, and porcine TASK-1 channels were heterologously expressed in Xenopus laevis oocytes. Two-electrode voltage clamp experiments were used for functional characterization. In murine models, among members of the K2P channel family, TASK-1 expression displayed highest levels in both atrial and ventricular tissue samples. Furthermore, K2P2.1, K2P5.1, and K2P6.1 showed significant expression levels. In CREM-transgenic mice, atrial expression of TASK-1 was significantly reduced in comparison with wild-type animals. In a murine model of TAC-induced pressure overload, ventricular TASK-1 expression remained unchanged, while atrial TASK-1 levels were significantly downregulated. When heterologously expressed in Xenopus oocytes, currents of murine, porcine, and human TASK-1 displayed similar characteristics. TASK-1 channels display robust cardiac expression in mice. Murine, porcine, and human TASK-1 channels share functional similarities. Dysregulation of atrial TASK-1 expression in murine AF and HF models suggests a mechanistic contribution to arrhythmogenesis.

Inverse remodelling of K2P3.1 K+ channel expression and action potential duration in left ventricular dysfunction and atrial fibrillation: implications for patient-specific antiarrhythmic drug therapy.

AIMS: Atrial fibrillation (AF) prevalence increases with advanced stages of left ventricular (LV) dysfunction. Remote proarrhythmic effects of ventricular dysfunction on atrial electrophysiology remain incompletely understood. We hypothesized that repolarizing K2P3.1 K+ channels, previously implicated in AF pathophysiology, may contribute to shaping the atrial action potential (AP), forming a specific electrical substrate with LV dysfunction that might represent a target for personalized antiarrhythmic therapy. METHODS AND RESULTS: A total of 175 patients exhibiting different stages of LV dysfunction were included. Ion channel expression was quantified by real-time polymerase chain reaction and Western blot. Membrane currents and APs were recorded from atrial cardiomyocytes using the patch-clamp technique. Severely reduced LV function was associated with decreased atrial K2P3.1 expression in sinus rhythm patients. In contrast, chronic (c)AF resulted in increased K2P3.1 levels, but paroxysmal (p)AF was not linked to significant K2P3.1 remodelling. LV dysfunction-related suppression of K2P3.1 currents prolonged atrial AP duration (APD) compared with patients with preserved LV function. In individuals with concomitant LV dysfunction and cAF, APD was determined by LV dysfunction-associated prolongation and by cAF-dependent shortening, respectively, consistent with changes in K2P3.1 abundance. K2P3.1 inhibition attenuated APD shortening in cAF patients irrespective of LV function, whereas in pAF subjects with severely reduced LV function, K2P3.1 blockade resulted in disproportionately high APD prolongation. CONCLUSION: LV dysfunction is associated with reduction of atrial K2P3.1 channel expression, while cAF leads to increased K2P3.1 abundance. Differential remodelling of K2P3.1 and APD provides a basis for patient-tailored antiarrhythmic strategies.

Upregulation of K(2P)3.1 K+ Current Causes Action Potential Shortening in Patients With Chronic Atrial Fibrillation.

BACKGROUND: Antiarrhythmic management of atrial fibrillation (AF) remains a major clinical challenge. Mechanism-based approaches to AF therapy are sought to increase effectiveness and to provide individualized patient care. K(2P)3.1 (TASK-1 [tandem of P domains in a weak inward-rectifying K+ channel-related acid-sensitive K+ channel-1]) 2-pore-domain K+ (K(2P)) channels have been implicated in action potential regulation in animal models. However, their role in the pathophysiology and treatment of paroxysmal and chronic patients with AF is unknown. METHODS AND RESULTS: Right and left atrial tissue was obtained from patients with paroxysmal or chronic AF and from control subjects in sinus rhythm. Ion channel expression was analyzed by quantitative real-time polymerase chain reaction and Western blot. Membrane currents and action potentials were recorded using voltage- and current-clamp techniques. K(2P)3.1 subunits exhibited predominantly atrial expression, and atrial K(2P)3.1 transcript levels were highest among functional K(2P) channels. K(2P)3.1 mRNA and protein levels were increased in chronic AF. Enhancement of corresponding currents in the right atrium resulted in shortened action potential duration at 90% of repolarization (APD90) compared with patients in sinus rhythm. In contrast, K(2P)3.1 expression was not significantly affected in subjects with paroxysmal AF. Pharmacological K(2P)3.1 inhibition prolonged APD90 in atrial myocytes from patients with chronic AF to values observed among control subjects in sinus rhythm. CONCLUSIONS: Enhancement of atrium-selective K(2P)3.1 currents contributes to APD shortening in patients with chronic AF, and K(2P)3.1 channel inhibition reverses AF-related APD shortening. These results highlight the potential of K(2P)3.1 as a novel drug target for mechanism-based AF therapy.

Therapeutic targeting of two-pore-domain potassium (K(2P)) channels in the cardiovascular system.

The improvement of treatment strategies in cardiovascular medicine is an ongoing process that requires constant optimization. The ability of a therapeutic intervention to prevent cardiovascular pathology largely depends on its capacity to suppress the underlying mechanisms. Attenuation or reversal of disease-specific pathways has emerged as a promising paradigm, providing a mechanistic rationale for patient-tailored therapy. Two-pore-domain K(+) (K(2P)) channels conduct outward K(+) currents that stabilize the resting membrane potential and facilitate action potential repolarization. K(2P) expression in the cardiovascular system and polymodal K2P current regulation suggest functional significance and potential therapeutic roles of the channels. Recent work has focused primarily on K(2P)1.1 [tandem of pore domains in a weak inwardly rectifying K(+) channel (TWIK)-1], K(2P)2.1 [TWIK-related K(+) channel (TREK)-1], and K(2P)3.1 [TWIK-related acid-sensitive K(+) channel (TASK)-1] channels and their role in heart and vessels. K(2P) currents have been implicated in atrial and ventricular arrhythmogenesis and in setting the vascular tone. Furthermore, the association of genetic alterations in K(2P)3.1 channels with atrial fibrillation, cardiac conduction disorders and pulmonary arterial hypertension demonstrates the relevance of the channels in cardiovascular disease. The function, regulation and clinical significance of cardiovascular K(2P) channels are summarized in the present review, and therapeutic options are emphasized.

A porcine large animal model of radiofrequency ablation-induced left bundle branch block.

Background: Electrocardiographic (ECG) features of left bundle branch (LBB) block (LBBB) can be observed in up to 20%-30% of patients suffering from heart failure with reduced ejection fraction. However, predicting which LBBB patients will benefit from cardiac resynchronization therapy (CRT) or conduction system pacing remains challenging. This study aimed to establish a translational model of LBBB to enhance our understanding of its pathophysiology and improve therapeutic approaches. Methods: Fourteen male pigs underwent radiofrequency catheter ablation of the proximal LBB under fluoroscopy and ECG guidance. Comprehensive clinical assessments (12-lead ECG, bloodsampling, echocardiography, electroanatomical mapping) were conducted before LBBB induction, after 7, and 21 days. Three pigs received CRT pacemakers 7 days after LBB ablation to assess resynchronization feasibility. Results: Following proximal LBB ablation, ECGs displayed characteristic LBBB features, including QRS widening, slurring in left lateral leads, and QRS axis changes. QRS duration increased from 64.2 ± 4.2 ms to 86.6 ± 12.1 ms, and R wave peak time in V6 extended from 21.3 ± 3.6 ms to 45.7 ± 12.6 ms. Echocardiography confirmed cardiac electromechanical dyssynchrony, with septal flash appearance, prolonged septal-to-posterior-wall motion delay, and extended ventricular electromechanical delays. Electroanatomical mapping revealed a left ventricular breakthrough site shift and significantly prolonged left ventricular activation times. RF-induced LBBB persisted for 3 weeks. CRT reduced QRS duration to 75.9 ± 8.6 ms, demonstrating successful resynchronization. Conclusion: This porcine model accurately replicates the electrical and electromechanical characteristics of LBBB observed in patients. It provides a practical, cost-effective, and reproducible platform to investigate molecular and translational aspects of cardiac electromechanical dyssynchrony in a controlled and clinically relevant setting.

Treatment of a Paroxysmal Atrioventricular Block by Implantation of a Bipolar, Single-Chamber Cardiac Pacemaker in a Donkey.

CASE SUMMARY: A two-year-old donkey presented with recurrent syncope. Electrocardiography revealed periods without any atrioventricular conduction and without any ventricular escape rhythm with a duration of up to one minute. Finally, atrioventricular conduction resumed spontaneously with a preceding ventricular escape beat. Laboratory tests and echocardiography identified no reversible cause. The diagnosis of a paroxysmal atrioventricular block (PAVB) was made. Therefore, a single-chamber cardiac pacemaker was implanted under general anesthesia. The device was programmed in the VVI mode to prevent further syncope. The therapy was considered successful as the donkey revealed no further syncope during the follow-up period of 17 months. CLINICAL RELEVANCE: Clinically relevant bradycardia is rare in equids. This is the first report to our knowledge to describe a PAVB, a term commonly used in human medicine, in a donkey. Detailed information about the diagnosis and the successful therapy is included, with a special focus on the implantation and programming of the permanent pacemaker.

Single beta-blocker or combined amiodarone therapy in implantable cardioverter-defibrillator and cardiac resynchronization therapy-defibrillator patients: Insights from the German DEVICE registry.

BACKGROUND: Because of its antiarrhythmic potency and due to the lack of alternatives, amiodarone is often used for antiarrhythmic therapy in patients with implantable cardioverter-defibrillator (ICD) or cardiac resynchronization therapy-defibrillator systems. To date, robust data on the safety and clinical benefit of amiodarone therapy in these patients are missing. OBJECTIVE: The purpose of this study was to assess the periprocedural and postprocedural outcomes of combined therapy with beta-blockers plus amiodarone compared to treatment with single beta-blockers in the "real-life" cohort of ICD recipients of the German DEVICE registry. METHODS: A total of 4499 patients who underwent ICD implantation, revision, or upgrade in 49 centers participating in the German DEVICE registry were enrolled from March 2007 to February 2014. RESULTS: Amiodarone had no significant effect on the success of defibrillation testing. Early implantation-associated complications were similar between the groups. However, 1-year overall mortality was significantly higher in the beta-blocker plus amiodarone cohort (adjusted hazard ratio 2.09; P <.001). Interestingly, among the surviving patients, amiodarone was not associated with a significantly reduced risk of ICD discharges or syncopal events. Furthermore, the occurrence of ventricular tachycardia (VT) storm or incessant VTs and the number of patients scheduled for intracardiac ablation did not differ among both groups, whereas the rate of rehospitalization was lower in the cohort with only beta-blockers. CONCLUSIONS: Although amiodarone has no adverse effect on the success of defibrillation testing, our data suggest an increased all-cause mortality under amiodarone therapy, especially in the subgroups of patients with sinus rhythm or severely reduced left ventricular function. In surviving patients, rates of arrhythmic events were comparable.

Case report of an S-ICD implantation for secondary prevention in a patient with complex congenital heart disease, dextrocardia, and situs solitus.

Background: Dextrocardia is a congenital anomaly in which the apex of the heart is abnormally located on the right side of the chest. Situs solitus describes viscera that are in the normal position, with the stomach on the left side. In these patients, implantation of transvenous implantable cardioverter-defibrillator (ICD) can be limited by anatomical abnormalities commonly associated with this condition. Case summary: We present the case of a young female patient with absent right atrioventricular connection, morphologically left systemic ventricle, muscular restrictive ventricular septal defect, and dextrocardia with situs solitus who was indicated for secondary prophylactic ICD implantation after resuscitation for polymorphic ventricular tachycardia. Due to a bilateral bidirectional Glenn anastomosis, transvenous access via the vena cava superior to the right ventricle could not be achieved. For this reason, we successfully implanted a subcutaneous ICD (S-ICD) with an individually optimized right parasternal electrode position. Potential complications of epimyocardial implantation via re-thoracotomy could thus be circumvented. Discussion: In patients with complex congenital heart disease, the S-ICD is an effective method of preventing sudden cardiac death. Our case report demonstrates the feasibility of left S-ICD implantation even in the presence of dextrocardia with situs solitus.

Simultaneous Quantification and Pharmacokinetic Characterization of Doxapram and 2-Ketodoxapram in Porcine Plasma and Brain Tissue.

Atrial fibrillation (AF) is an arrhythmia associated with an increased stroke risk and mortality rate. Current treatment options leave unmet needs in AF therapy. Recently, doxapram has been introduced as a possible new option for AF treatment in a porcine animal model. To better understand its pharmacokinetics, three German Landrace pigs were treated with intravenous doxapram (1 mg/kg). Plasma and brain tissue samples were collected. For the analysis of these samples, an ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) assay for the simultaneous measurement of doxapram and its active metabolite 2-ketodoxapram was developed and validated. The assay had a lower limit of quantification (LLOQ) of 10 pg/mL for plasma and 1 pg/sample for brain tissue. In pigs, doxapram pharmacokinetics were biphasic with a terminal elimination half-life (t1/2) of 1.38 ± 0.22 h and a maximal plasma concentration (cmax) of 1780 ± 275 ng/mL. Its active metabolite 2-ketodoxapram had a t1/2 of 2.42 ± 0.04 h and cmax of 32.3 ± 5.5 h after administration of doxapram. Protein binding was 95.5 ± 0.9% for doxapram and 98.4 ± 0.3% for 2-ketodoxapram with a brain-to-plasma ratio of 0.58 ± 0.24 for doxapram and 0.12 ± 0.02 for 2-ketodoxapram. In conclusion, the developed assay was successfully applied to the creation of pharmacokinetic data for doxapram, possibly improving the safety of its usage.

MicroRNAs Regulate TASK-1 and Are Linked to Myocardial Dilatation in Atrial Fibrillation.

Background Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. However, underlying molecular mechanisms are insufficiently understood. Previous studies suggested that microRNA (miRNA) dependent gene regulation plays an important role in the initiation and maintenance of AF. The 2-pore-domain potassium channel TASK-1 (tandem of P domains in a weak inward rectifying K+ channel-related acid sensitive K+ channel 1) is an atrial-specific ion channel that is upregulated in AF. Inhibition of TASK-1 current prolongs the atrial action potential duration to similar levels as in patients with sinus rhythm. Here, we hypothesize that miRNAs might be responsible for the regulation of KCNK3 that encodes for TASK-1. Methods and Results We selected miRNAs potentially regulating KCNK3 and studied their expression in atrial tissue samples obtained from patients with sinus rhythm, paroxysmal AF, or permanent/chronic AF. MiRNAs differentially expressed in AF were further investigated for their ability to regulate KCNK3 mRNA and TASK-1 protein expression in human induced pluripotent stem cells, transfected with miRNA mimics or inhibitors. Thereby, we observed that miR-34a increases TASK-1 expression and current and further decreases the resting membrane potential of Xenopus laevis oocytes, heterologously expressing hTASK-1. Finally, we investigated associations between miRNA expression in atrial tissues and clinical parameters of our patient cohort. A cluster containing AF stage, left ventricular end-diastolic diameter, left ventricular end-systolic diameter, left atrial diameter, atrial COL1A2 (collagen alpha-2(I) chain), and TASK-1 protein level was associated with increased expression of miR-25, miR-21, miR-34a, miR-23a, miR-124, miR-1, and miR-29b as well as decreased expression of miR-9 and miR-485. Conclusions These results suggest an important pathophysiological involvement of miRNAs in the regulation of atrial expression of the TASK-1 potassium channel in patients with atrial cardiomyopathy.

Treatment of atrial fibrillation with doxapram: TASK-1 potassium channel inhibition as a novel pharmacological strategy.

AIMS: TASK-1 (K2P3.1) two-pore-domain potassium channels are atrial-specific and significantly up-regulated in atrial fibrillation (AF) patients, contributing to AF-related electrical remodelling. Inhibition of TASK-1 in cardiomyocytes of AF patients was shown to counteract AF-related action potential duration shortening. Doxapram was identified as a potent inhibitor of the TASK-1 channel. In this study, we investigated the antiarrhythmic efficacy of doxapram in a porcine model of AF. METHODS AND RESULTS: Doxapram successfully cardioverted pigs with artificially induced episodes of AF. We established a porcine model of persistent AF in domestic pigs via intermittent atrial burst stimulation using implanted pacemakers. All pigs underwent catheter-based electrophysiological investigations prior to and after 14 days of doxapram treatment. Pigs in the treatment group received intravenous administration of doxapram once per day. In doxapram-treated AF pigs, the AF burden was significantly reduced. After 14 days of treatment with doxapram, TASK-1 currents were still similar to values of sinus rhythm animals. Doxapram significantly suppressed AF episodes and normalized cellular electrophysiology by inhibition of the TASK-1 channel. Patch-clamp experiments on human atrial cardiomyocytes, isolated from patients with and without AF could reproduce the TASK-1 inhibitory effect of doxapram. CONCLUSION: Repurposing doxapram might yield a promising new antiarrhythmic drug to treat AF in patients.