Introduction

Effective and safe pharmacologic treatment of atrial and ventricular arrhythmias remains an unmet need in cardiovascular medicine. Shortening of refractory periods promotes electrical re-entry that underlies atrial fibrillation (AF) and ventricular tachycardia (VT) (Tomaselli and Marbán 1999; Soucek et al. 2012; Trappe et al. 2013). Rhythm control may be achieved by impairment of electrical re-entry through cardiac K+ current inhibition by class III antiarrhythmic drugs. Two-pore-domain potassium (K2P) channels mediate K+ background currents that stabilize the negative resting membrane potential and contribute to action potential (AP) repolarization in excitable cells (Goldstein et al. 2001; Marban 2002). K2P currents are regulated through polymodal mechanisms (Goldstein et al. 2001; Enyedi and Czirják 2010; Sandoz et al. 2011, 2012; Staudacher et al. 2011a, b; Gierten et al. 2012; Schmidt et al. 2012, 2017; Seyler et al. 2014a).

K2P17.1 channels (tandem of P domains in a weak inward rectifying K+ channel (TWIK)-related acid sensitive K+ (TASK) 4 channels, or TWIK-related alkaline pH-activated K+ (TALK) 2 channels) are expressed in the human heart, predominantly in the atria (Decher et al. 2001; Girard et al. 2001; Schmidt et al. 2015). Atrial K2P17.1 abundance is reduced in patients with heart failure (HF) or AF (Schmidt et al. 2017). The association between a genetic K2P17.1 variant and ischemic stroke in Caucasians but not in a Chinese cohort (Domingues-Montanari et al. 2010; Ma et al. 2013) further indicates a potential contribution of K2P17.1 function to AF pathophysiology. In addition, K2P17.1 expression is suppressed in human left ventricular tissue obtained from HF patients compared to patients with preserved cardiac function (Chai et al. 2017). Duration of atrial and ventricular action potentials (AP) is prolonged in patients with HF (Tomaselli and Marbán 1999; Schmidt et al. 2017), consistent with reduction of repolarizing K+ currents. By contrast, cardiac K2P17.1 current was enhanced in patients carrying a K2P17.1 channel gain-of-function mutation associated with cardiac conduction disease (K2P17.1 G88R; Friedrich et al. 2014).

K2P17.1 currents are increased upon extracellular alkalization and blocked by barium (Decher et al. 2001; Kang and Kim 2004; Duprat et al. 2005; Niemeyer et al. 2007). Changes in K2P17.1 expression and function regulate action potential duration (APD) of cardiac myocytes: expression of the K2P17.1 G88R gain-of-function mutant results in APD shortening in HL-1 murine atrial myocytes (Friedrich et al. 2014), whereas siRNA-mediated knockdown of repolarizing K2P17.1 current causes APD prolongation in cardiomyocytes derived from human-induced pluripotent stem cells (Chai et al. 2017). Pharmacologic modulation of K2P17.1 current levels may be employed to suppress atrial and ventricular arrhythmias. The development of this emerging therapeutic principle into clinical practice is limited by the lack of pharmacologic data. This study provides a systematic assessment of K2P17.1 regulation by clinically used antiarrhythmic compounds to close this scientific and translational gap. Activation of the channels by the class I antiarrhythmic drug propafenone was mechanistically studied in detail.

Methods

Patients

A total of 5 patients (mean age, 69 ± 4.1 years; male/female, 4/1) with sinus rhythm (SR) undergoing open heart surgery for coronary artery bypass grafting and/or valve replacement were included (Table 1). Tissue samples were obtained from right atrial appendages.

Table 1 Baseline characteristics of patients subjected to analysis of atrial K2P17.1 protein expression
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Molecular biology

Amplification of KCNK17 cDNA encoding human K2P17.1 protein (GenBank accession number EU978944) was described previously (Gierten et al. 2008). For in vitro transcription, human KCNK17 was subcloned into pRAT, a dual-purpose expression vector containing a CMV promoter for mammalian expression and a T7 promoter for cRNA synthesis. Plasmids were linearized with NotI and transcribed using the T7 mMessage mMachine kit (Ambion, Austin, TX, USA). RNA transcripts were quantified by spectrophotometry and cRNA integrity was assessed by agarose gel electrophoresis (Thomas et al. 2008).

Xenopus laevis oocyte preparation

Ovarian lobes were surgically removed in aseptic technique from female Xenopus laevis frogs anesthetized with 1 g/l tricaine solution (pH = 7.5). Frogs were not fed on the day of surgery to avoid emesis during anesthesia. After surgery, the frogs were allowed to recover consciousness, followed by at least 2-month recovery without surgery. Oocyte collection was alternated between left and right ovaries, and no more than four surgeries were performed on one individual frog. After the final collection of oocytes, the anesthetized frog was killed by decerebration and pithing. Following collagenase treatment (collagenase A or D; Roche Diagnostics, Mannheim, Germany), stage V–VI defolliculated oocytes were manually isolated under a stereomicroscope. For electrophysiological recordings, complementary (c)RNA (1.5–5 ng, 46 nl/oocyte) encoding human K2P17.1 was injected. For Western blot studies, 1.5 or 3 ng encoding human KCNK17 cRNA was injected (46 nl/oocyte).

Western blot analysis

Protein immunodetection was performed by sodium dodecyl sulfate (SDS) gel electrophoresis and Western blotting as described (Bikou et al. 2011; Trappe et al. 2013; Schmidt et al. 2015). Tissue sections obtained from human right atrial samples were rinsed in phosphate-buffered saline (PBS), rapidly frozen in liquid nitrogen and stored at − 80 °C. Aliquots were then homogenized (TissueRuptor, QIAGEN, Hilden, Germany) in radioimmunoprecipitation (RIPA) lysis buffer containing 50 mM Tris-HCl (pH 7.4), 0.5% NP-40, 0.25% sodium deoxycholate, 150 mM NaCl, 1 mM EDTA, 1 mM Na3VO4, 1 mM NaF, and protease inhibitors (Complete; Roche, Indianapolis, IN, USA).

To obtain Xenopus oocyte protein, 150 oocytes of each study group were harvested. Protein extracts were homogenized in a buffer containing 100 mM NaCl, 40 mM KCl, 1 mM ethylene-diamine-tetraacetic acid (EDTA), Complete Protease Inhibitor Cocktail (Roche Diagnostics, Indianapolis, USA), 10% glycerol, 1% 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), 20 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (pH 7.4), and clarified by repeated centrifugations. The supernatant was diluted with 2-mercaptoethanol-containing loading buffer and subjected to Western blotting.

The protein concentration was determined using the bicinchoninic acid (BCA) protein assay (Thermo Scientific, Rockford, IL, USA), and equal amounts of protein were separated on SDS polyacrylamide gels. Nitrocellulose membranes were developed by sequential exposure to blocking reagent containing 5% dry milk (supplemented with 3% bovine serum albumin for oocyte experiments), primary antibodies directed against K2P17.1 (1:200; ab198043, Abcam, Cambridge, UK), and appropriate HRP-conjugated secondary antibodies (1:3000; ab6802; Abcam). Signals were developed using the enhanced chemiluminescence assay (ECL Western Blotting Reagents, GE Healthcare, Buckinghamshire, UK) and quantified with ImageJ 1.41 Software (National Institutes of Health, Bethesda, MD, USA). Protein content was normalized to glyceraldehyde 3-phosphate dehydrogenase (GAPDH) using anti-GAPDH primary antibodies (1:10,000; G8140-01; US Biological, Swampscott, MA, USA for human tissue; 1:10,000; ab181602; Abcam for oocyte protein) and corresponding secondary antibodies (1,3000; sc-2005; Santa Cruz Biotechnology) for quantification of optical density.

Cell culture

Chinese hamster ovary (CHO) cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM; Invitrogen, Karlsruhe, Germany) supplemented with 10% fetal bovine serum (Invitrogen), 100 U/ml penicillin G sodium, and 100 μg/ml streptomycin sulfate in an atmosphere of 95% humidified air and 5% CO2 at 37 °C. Cells were passaged regularly and subcultured prior to treatment. KCNK17 was expressed using transient transfections in CHO cells. The total DNA transfected was equal to 2.0 μg for both conditions (1.8 μg of KCNK17 + 0.2 μg of yellow fluorescent protein (YFP) to identify transfected cells). Transfection of CHO cells was accomplished using Lipofectamine 2000 (Life Technologies, Grand Island, NY, USA) according to the manufacturer’s protocol, using 35-mm dishes.

Electrophysiology

Two-electrode voltage clamp measurements were performed to record whole cell currents from Xenopus laevis oocytes 3–4 days after cRNA injection as described (Thomas et al. 2008; Gierten et al. 2012). Two-electrode voltage clamp electrodes were pulled from 1 mm borosilicate glass tubes (Science Products, Hofheim, Germany) using a P-87 micropipette puller (Sutter Instruments, Novato, CA, USA). Macroscopic currents were recorded using an Oocyte Clamp amplifier OC-725C (Warner Instruments, Hamden, CT, USA) and pClamp software (Molecular Devices, Sunnyvale, CA, USA). Data were sampled at 2 kHz and low-pass filtered at 1 kHz. Leak currents were not subtracted. Current amplitudes were determined at the end of + 20-mV voltage pulses unless stated otherwise. Voltage clamp measurements were carried out at room temperature (20–22 °C). Voltage clamp electrodes filled with 3 M KCl solution had tip resistances of 1.5–3 MΩ. Experiments were performed under constant perfusion by a gravity-driven perfusion system. The standard extracellular bath solution contained 96 mM NaCl, 4 mM KCl, 1.1 mM CaCl2, 1 mM MgCl2, and 5 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES). The pH was adjusted with NaOH to pH 8.5 to activate human K2P17.1 currents (Decher et al. 2001; Seyler et al. 2014a).

Currents were recorded from CHO cells with the whole cell patch-clamp technique using an Axopatch 200B amplifier and a Digidata 1440A (both from Molecular Devices). Voltage-clamp command pulses were inputted using pCLAMP version 10 (Molecular Devices). Patch-clamp pipettes were pulled from 8161 Corning borosilicate capillary glass (Dow-Corning, Midland, MI, USA) and polished. Tip resistances ranged from 1.0 to 2.2 MΩ. The extracellular bath solution contained (in mM at pH 8.5 adjusted with NaOH) 140 NaCl, 5 KCl, 1 MgCl2, 1.8 CaCl2, 10 HEPES, and 10 glucose. The intracellular pipette solution contained (in mM at pH 7.2 adjusted with KOH) 100 K-aspartate, 20 KCl, 2 MgCl2, 1 CaCl2, 10 EGTA, 2 ATP, and 10 HEPES. Of note, no difference in K2P17.1 current density was observed using HEPES or AMPSO (((1,1-dimethyl-2-hydroxyethyl)amino)-2-hydroxypropanesulfonic acid sodium salt) to adjust extracellular pH to 8.5, respectively (data not shown). Patch clamp recordings were performed at 23 °C.

Drugs

Drugs were obtained from Sigma-Aldrich (Steinheim, Germany), unless indicated otherwise. Ajmaline (abcr, Karlsruhe, Germany), amiodarone, carvedilol, mexiletine, propafenone, propranolol, sotalol, and quinidine were dissolved in dimethyl sulfoxide (DMSO) to 100 mM stock solutions. Metoprolol was dissolved in H2O to a 100 mM stock solution. Ranolazine was dissolved in H2O to a 10 mM stock solution. Amitriptyline and verapamil were dissolved in methanol to 100 mM stock solutions. Stock solutions were stored at − 20 °C. Aliquots of the stock solutions were diluted to the desired concentration with the bath solution on the day of experiments.

Data analysis and statistics

PCLAMP 8.2 (Axon Instruments, Foster City, USA), Origin 8 (OriginLab, Northampton, MA, USA), Prism 6.0 (GraphPad, La Jolla, CA, USA) and Excel (Microsoft, Redmond, WA, USA) software was used for data acquisition and analysis. Concentration-response relationships for drug-induced activation were fit with a Hill equation of the following form: y = Imin + (Imax − Imin) × EC50n/(EC50n + xn), where I indicates current, n is the Hill coefficient, and EC50 is the concentration necessary for half-maximal activation. Data are expressed as mean ± standard error of the mean (SEM). Paired and unpaired Student’s t tests (two-tailed tests) were applied to compare statistical significance of the results. P < 0.05 was considered as statistically significant.

Results

K2P17.1 expression in human atrium

K2P17.1 protein was expressed in human atrium (Fig. 1a). This finding is consistent with previous studies reporting predominant atrial expression of KCNK17 mRNA or K2P17.1 protein (Decher et al. 2001; Girard et al. 2001; Schmidt et al. 2015, 2017) and highlights potential physiological significance of K2P17.1 currents in atrial electrophysiology and arrhythmogenesis. Specific detection of recombinant human K2P17.1 protein expressed in Xenopus laevis oocytes and the lack of anti-K2P17.1 immunoreactivity in uninjected oocytes, indicating specificity of the antibodies used (Fig. 1b).

Fig. 1
figure 1

Western blot analysis of K2P17.1 protein. a Representative immunoblots obtained from right atrial appendages (RAA) of five patients undergoing cardiac surgery, probed with anti-K2P17.1 antibodies. b Protein lysates from Xenopus oocytes heterologously expressing human K2P17.1 protein (1.5 or 3 ng RNA/oocyte as indicated) and from uninjected (uninj.) control oocytes served as positive and negative controls, respectively. Lower panels, anti-glyceraldehyde 3-phosphate dehydrogenase (GAPDH) antibodies were applied to confirm equal protein load

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Regulation of K2P17.1 function by antiarrhythmic drugs

Electropharmacology of K2P17.1 channels was assessed using the Xenopus laevis oocyte system and two-electrode voltage-clamp electrophysiology. For screening experiments, supratherapeutic concentrations were applied to ensure the detection of any potential drug-channel interactions. From a holding potential of − 80 mV, test pulses were applied for 500 ms to voltages between − 140 and + 80 mV in 20 mV increments (0.5 Hz) (Fig. 2). Current amplitudes were measured at the end of the + 20 mV pulse before and after drug application for 60 min (Fig. 2a–n). K2P17.1 currents were activated by antiarrhythmic drugs quinidine (+ 57.7 ± 12.2%; n = 5; p = 0.009; 100 μM), mexiletine (+ 20.6 ± 4.0%; n = 6; p = 0.0002; 100 μM), propafenone (+ 296.1 ± 39.2%; n = 6; p = 0.001; 100 μM), metoprolol (+ 17.3 ± 3.6%; n = 6; p = 0.009; 100 μM), and propranolol (+ 139.2 ± 22.7%; n = 6; p = 0.005; 100 μM), respectively (Figs. 2b–d, f, g and 3). By contrast, K2P17.1 current amplitudes were reduced upon application of sotalol (− 9.8 ± 1.8%; n = 5; p = 0.008; 100 μM), amiodarone (− 12.5 ± 4.2%; n = 6; p = 0.010), verapamil (− 20.5 ± 4.5%; n = 5; p = 0.013; 100 μM), and ranolazine (− 8.3 ± 1.1%; n = 6; p = 0.012; 100 μM) (Figs. 2h–k and 3). For comparison, the antidepressant amitriptyline that harbors proarrhythmic potential through inhibition of cardiac K+ currents (Witchel et al. 2003) was studied. Amitriptyline did not significantly affect K2P17.1 current amplitudes (− 7.9 ± 3.8%; n = 5; p = 0.088; 100 μM) (Figs. 2l and 3). Application of the solvent DMSO (60 min; 0.1% v/v) did not significantly affect mean K2P current amplitudes (+ 0.8 ± 3.2%; n = 5; p = 0.47) (Figs. 2m and 3), while the solvent methanol (0.1% v/v) resulted in weak current activation (+ 9.7 ± 2.5%; n = 6; p = 0.008) within 60 min (Figs. 2n and 3). Of note, methanol was used as solvent for verapamil and amitriptyline only. Considering 9.7% activation of K2P17.1 currents after 60 min methanol application and 20.5% (verapamil) or 7.9% (amitriptyline) inhibition compared with drug-free control conditions, the total degree of K2P17.1 inhibition amounts to 30.2% (verapamil; p = 0.001 versus methanol) or 17.6% (amitriptyline; p = 0.006 vs. methanol), respectively.

Fig. 2
figure 2

Pharmacology of human K2P17.1 potassium channels expressed in Xenopus oocytes. Representative macroscopic currents recorded under control conditions and after drug application (60 min, left panels) with time courses of K2P17.1 current modulation at + 20 mV membrane potential (right panels) are displayed for ajmaline (a), quinidine (b), mexiletine (c), propafenone (d), carvedilol (e), metoprolol (f), propranolol (g), sotalol (h), amiodarone (i), verapamil (j), ranolazine (k), and amitriptyline (l). The solvents dimethyl sulfoxide (DMSO; m) and methanol (n) were studied for comparison

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Fig. 3
figure 3

Comparison of activating and inhibitory drug effects on K2P17.1. Currents recorded from Xenopus oocytes were quantified at + 20 mV membrane voltage after application of indicated compounds for 60 min. Values are provided normalized to control conditions prior to administration of the respective drugs. Data are given as mean ± SEM; *p < 0.05, **p < 0.01, ***p < 0.001 versus drug-free control measurements (n = 5 to 6 cells)

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Biophysical analysis of K2P17.1 activation by propafenone

Biophysical characteristics of K2P17.1 current enhancement by propafenone, the drug-K2P17.1 channel interaction with most pronounced functional effects, were studied in more detail using the Xenopus oocyte expression system. Currents were recorded as described in Fig. 2 and quantified at + 20 mV after propafenone administration for 60 min. The onset of activation is shown in Fig. 2d (n = 6). After a control period of 30 min showing stable current levels, K2P17.1 current activation by 100 μM propafenone developed rapidly. To assess the concentration dependence of hK2P17.1 activation by propafenone, currents in the presence of the drug were normalized to their respective control values and plotted as relative current amplitudes in Fig. 4a (n = 3 to 6 cells were investigated at each concentration). The half-maximal effective concentration (EC50) for activation of K2P17.1 channels was 75.4 ± 0.53 μM with a Hill coefficient nH of 9.1 ± 0.15.

Fig. 4
figure 4

Pharmacological and biophysical analysis of K2P17.1 activation by propafenone. a Concentration-response relationships for the effect of propafenone on human K2P17.1 currents measured in Xenopus oocytes at the end of the + 20 mV voltage step after 60 min drug application (n = 3 to 6 cells). The EC50 value yielded 75.4 μM. b–e Effects of propafenone on hK2P17.1 voltage-dependence of activation. Control measurement (b) and the effect of 100 μM propafenone (60 min; c) are shown in one representative oocyte; d and e display activation curves, i.e., step current amplitudes as function of test potentials, recorded under isochronal conditions (d original current amplitudes; e values normalized to maximum currents) (n = 6). Data are provided as mean ± SEM

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Drug effects on K2P17.1 current voltage (I-V) relationship were investigated under isochronal recording conditions using the protocol described above. Representative families of current traces from one cell are shown for control conditions (Fig. 4b) and after application of 100 μM propafenone for 60 min (Fig. 4c). The current-voltage relationship was not affected by propafenone administration (Fig. 4d, e). Mean half-maximal activation voltage (V1/2) normalized to current amplitudes recorded at + 60 mV was 11.2 ± 1.1 mV under control conditions and yielded 11.7 ± 1.4 mV (n = 5; p = 0.84) in the presence of propafenone.

Propafenone-induced K2P17.1 current enhancement in mammalian cells

We expressed hK2P17.1 potassium channels in Chinese hamster ovary (CHO) cells to demonstrate modulation of K2P17.1 currents in mammalian cells (Fig. 5). From a holding potential of − 80 mV, depolarizing pulses were applied for 500 ms to voltages between − 120 and + 80 mV in 20-mV increments (Fig. 5a, b). Propafenone (100 μM, 30 min) activated K2P17.1 currents by 7.8-fold (n = 6–13; p < 0.0001) (Fig. 5c). Concentration-dependent activation was analyzed at + 20 mV after propafenone application for 30 min (Fig. 5d). The half-maximal activating concentration could not be calculated as maximum activation was not reached with the highest concentration applied without compromising CHO cell integrity.

Fig. 5
figure 5

Propafenone-induced activation of human K2P17.1 channels expressed in Chinese hamster ovary (CHO) cells. Families of current traces recorded under control conditions and after superfusion with 100 μM propafenone were normalized to capacitance and are displayed in a and b, respectively. c Mean activation curves obtained under control conditions and after application of 100 μM propafenone (n = 5). d Concentration-response relationships for the effect of propafenone on hK2P17.1 currents measured at + 20 mV (n = 3 to 7 cells; mean ± SEM)

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Discussion

Cardiovascular pharmacology of human K2P17.1 K+ channels: comparison with previous studies

The present work reveals that human cardiac K2P17.1 background K+ channels are previously unrecognized targets for multiple antiarrhythmic drugs. K2P17.1 currents were activated by class I antiarrhythmic compounds (quinidine, mexiletine, propafenone) and by β-blockers (metoprolol, propranolol). By contrast, class III drugs (amiodarone, sotalol), a class IV compound (verapamil), and the late sodium current inhibitor, ranolazine, inhibited K2P17.1. There is, however, no uniform class effect of antiarrhythmics on K2P17.1 function, as other class I (ajmaline, flecainide) or III drugs (dronedarone) as well as β-blockers (carvedilol) did not affect K2P17.1 current amplitudes or even induced opposite effects (e.g., K2P17.1 activation by the class III drug vernakalant) here and in prior studies (Table 2). Among drugs investigated, quinine and quinidine displayed both inhibitory and activating actions on K2P17.1 channels in independent studies (Table 2). While these differences cannot be fully resolved based on available data, we may speculate that different experimental conditions determined whether quinine and quinidine caused activation or inhibition of K2P17.1, respectively.

Table 2 Electropharmacology of K2P17.1 channels: inhibitory and activating effects of antiarrhythmic compounds
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K2P17.1 channel activation or inhibition occurred at concentrations exceeding free plasma levels (Table 2), indicating low clinical significance of K2P17.1 modulation during clinical application of the respective drugs with current dosing recommendations. Therefore, associations between in vitro modulation of K2P17.1 and clinical effects cannot be established at the present, early stage of K2P17.1 pharmacology research. However, impaired metabolism may result in significantly higher plasma levels and in modulation of K2P17.1 channel function during drug administration. Although novel pharmacological interactions reported here may not affect cardiac cellular electrophysiology in routine clinical practice, differential actions of antiarrhythmic drugs on K2P17.1 channels provide the basis for future research and development aimed at the identification of more potent and selective K2P17.1 modulators. A comparison of multiple different chemical structures described here as K2P17.1 blockers or activators is expected to support the targeted design of novel compounds.

Mechanism of K2P17.1 current activation by propafenone

The rapid onset of activation indicates a direct drug–channel interaction and provides evidence against decreased protein turnover or impaired protein degradation as molecular mechanism of action. The Hill coefficient of 9.1 may indicate multiple binding sites for propafenone within the K2P17.1 channel protein with positively cooperative binding. K2P17.1 current–voltage relationships were not altered by propafenone, indicating that protein domains responsible for voltage sensing were not directly affected. Of note, biophysical characteristics of K2P17.1 activation by propafenone are shared with those observed with vernakalant, a class III drug previously reported to activate K2P17.1 (Seyler et al. 2014b), suggesting a common molecular mechanism of current activation that remains to be elucidated in more detail in future studies.

Clinical significance of pharmacologic K2P17.1 current activation and inhibition—implications for therapy

Complex and heterogenous mechanisms of cardiac arrhythmia require differential antiarrhythmic therapy with appropriate approaches. The “classical” mechanism of atrial arrhythmogenesis in AF involves reduced electrical conduction velocity and shortening of atrial action potential duration (APD) and effective refractory periods (AERPs) that perpetuate AF through promotion of electrical reentry (Schotten et al. 2011). These alterations are observed in patients with persistent or permanent AF that do not exhibit severe HF (Schmidt et al. 2017). At the molecular level, increased potassium currents are primarily responsible for shortening of refractoriness (Schotten et al. 2011; Schmidt et al. 2015, 2017). In these cases, inhibition of repolarizing K2P17.1 currents that are substantially expressed in human atrium may be effective to suppress AF. By contrast, atrial action potentials are shortened and K2P17.1 expression is reduced in patients with HF (Schmidt et al. 2017). Furthermore, ventricular electrical remodeling is similarly characterized by prolonged ventricular refractoriness and reduced K+ channel abundance including K2P17.1 (Tomaselli and Marbán 1999; Nattel et al. 2007; Chai et al. 2017). Here, activation of K2P17.1 channels may be employed as antiarrhythmic principle. Whether in vitro membrane hyperpolarization through K2P17.1 activation may suppress automaticity and triggered activity in vivo remains to be confirmed in future studies using specific, high-affinity activators and appropriate animal models.

Conclusion

Cardiac K2P17.1 channels are differentially regulated by multiple antiarrhythmic drugs. This work highlights a mechanistic link between modulation of cardiac K2P17.1 K+ currents and antiarrhythmic therapy. In addition, the data provide a molecular starting point for the development of future, mechanism-derived antiarrhythmic concepts targeting individual K2P17.1 dysfunction in cardiac arrhythmia. The therapeutic significance of cardiac K2P17.1 channel blockade or activation in specific heart rhythm disorders requires validation in translational and clinical investigations.