Cardiac K2P13.1 (THIK-1) two-pore-domain K+ channels: Pharmacological regulation and remodeling in atrial fibrillation.

Cardiac two-pore-domain potassium (K2P) channels have been proposed as novel antiarrhythmic targets. K2P13.1 (THIK-1) channels are expressed in the human heart, and atrial K2P13.1 levels are reduced in patients with atrial fibrillation (AF) or heart failure. The first objective of this study was to investigate acute effects of antiarrhythmic drugs on human K2P13.1 currents. Second, we assessed atrial K2P13.1 remodeling in AF pigs to validate the porcine model for future translational evaluation of K2P13.1-based antiarrhythmic concepts. K2P13.1 protein expression was studied in domestic pigs during AF induced by atrial burst pacing. AF was associated with 66% reduction of K2P13.1 levels in the right atrium at 21-day follow-up. Voltage clamp electrophysiology was employed to elucidate human K2P13.1 channel pharmacology in Xenopus oocytes. Propafenone (-26%; 100 µM), mexiletine (-75%; 1.5 mM), propranolol (-38%; 200 µM), and lidocaine (-59%; 100 µM) significantly inhibited K2P13.1 currents. By contrast, K2P13.1 channels were not markedly affected by quinidine, carvedilol, metoprolol, amiodarone and verapamil. Concentration-dependent K2P13.1 blockade by mexiletine occurred rapidly with membrane depolarization and was frequency-independent. Mexiletine reduced K2P13.1 open rectification properties and shifted current-voltage relationships towards more negative potentials. In conclusion, atrial expression and AF-associated downregulation of K2P13.1 channels in a porcine model resemble human findings and support a general role for K2P13.1 in AF pathophysiology. K2P13.1 current sensitivity to antiarrhythmic drugs provides a starting point for further development of an emerging antiarrhythmic paradigm.

Cloning and characterization of zebrafish K2P13.1 (THIK-1) two-pore-domain K+ channels.

Two-pore-domain potassium (K2P) channels conduct background potassium currents in the heart and other tissues. K2P currents are involved in the repolarization of action potentials and stabilize the resting membrane potential. Human K2P13.1 (THIK-1) channels are expressed in the heart and have recently been implicated in atrial fibrillation. The in vivo significance of K2P13.1 currents in cardiac electrophysiology is not known. We hypothesized that Danio rerio (zebrafish) may serve as model to elucidate the functional role of cardiac K2P13.1 channels. This work was designed to characterize zebrafish orthologs of K2P13.1. Two zkcnk13 coding sequences were identified by DNA database searches and amplified from zebrafish cDNA. Human and zebrafish K2P13.1 proteins exhibit 70% (K2P13.1a) and 66% (K2P13.1b) identity. Kcnk13 expression in zebrafish was studied using polymerase chain reaction. Zebrafish kcnk13a and zkcnk13b mRNAs were detected in brain and heart. Human and zebrafish K2P13.1 currents were analyzed in the Xenopus oocyte expression system by voltage clamp electrophysiology. Zebrafish K2P13.1a polypeptides were non-functional, while zK2P13.1b channels exhibited K+ selective, outwardly rectifying currents. Zebrafish and human K2P13.1 currents were similarly activated by arachidonic acid and reduced by barium, mexiletine, lidocaine, and inhibition of phospholipase C. In conclusion, zebrafish K2P13.1b channels and their human orthologs exhibit structural and regulatory similarities. Zebrafish may be used as in vivo model for the assessment of physiology and therapeutic significance of K2P13.1.

Cardiovascular pharmacology of K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels.

K2P17.1 (TASK-4, TALK-2) potassium channels are expressed in the heart and represent potential targets for pharmacological management of atrial and ventricular arrhythmias. Reduced K2P17.1 expression was found in atria and ventricles of heart failure (HF) patients. Modulation of K2P17.1 currents by antiarrhythmic compounds has not been comprehensively studied to date. The objective of this study was to investigate acute effects of clinically relevant antiarrhythmic drugs on human K2P17.1 channels to provide a more complete picture of K2P17.1 electropharmacology. Whole-cell patch clamp and two-electrode voltage clamp electrophysiology was employed to study human K2P17.1 channel pharmacology. K2P17.1 channels expressed in Xenopus laevis oocytes were screened for sensitivity to antiarrhythmic drugs, revealing significant activation by propafenone (+ 296%; 100 µM), quinidine (+ 58%; 100 µM), mexiletine (+ 21%; 100 µM), propranolol (+ 139%; 100 µM), and metoprolol (+ 17%; 100 µM) within 60 min. In addition, the currents were inhibited by amiodarone (- 13%; 100 µM), sotalol (- 10%; 100 µM), verapamil (- 21%; 100 µM), and ranolazine (- 8%; 100 µM). K2P17.1 channels were not significantly affected by ajmaline and carvedilol. Concentration-dependent K2P17.1 activation by propafenone was characterized in more detail. The onset of activation was fast, and current-voltage relationships were not modulated by propafenone. K2P17.1 activation was confirmed in mammalian Chinese hamster ovary cells, revealing 7.8-fold current increase by 100 µM propafenone. Human K2P17.1 channels were sensitive to multiple antiarrhythmic drugs. Differential pharmacological regulation of repolarizing K2P17.1 background K+ channels may be employed for personalized antiarrhythmic therapy.

Identification and functional characterization of zebrafish K2P17.1 (TASK-4, TALK-2) two-pore-domain K+ channels.

Human K2P17.1 (TASK-4, TALK-2) two-pore-domain potassium (K2P) channels have recently been implicated in heart rhythm disorders including atrial fibrillation and conduction disease. The functional in vivo significance of K2P17.1 currents in cardiac electrophysiology remains incompletely understood. Danio rerio (zebrafish) may be utilized to elucidate the role of cardiac K2P channels in vivo. The aim of this work was to identify and characterize the zebrafish ortholog of K2P17.1 in comparison to its human counterpart. The zkcnk17 coding sequence was amplified from zebrafish cDNA. Zebrafish kcnk17 mRNA expression was assessed by polymerase chain reaction. Human and zebrafish K2P17.1 currents were analyzed using two-electrode voltage clamp electrophysiology and the Xenopus oocyte expression system. Kcnk17 mRNA was detected in zebrafish brain. Human and zebrafish K2P17.1 proteins exhibited 33.4% identity. Zebrafish K2P17.1 channels conducted K+ selective currents with open rectification properties. Both human and zebrafish K2P17.1 were inhibited by barium. In contrast to human K2P17.1, zK2P17.1 currents were not sensitive to extracellular alkalization, likely due to the lack of a lysine residue involved in pH sensing of hK2P17.1. In conclusion, zebrafish and human K2P17.1 channels display similar structural and regulatory properties. Zebrafish may serve as an in vivo model to study neuronal K2P17.1 function but does not appear appropriate for cardiac electrophysiology studies. Differences in pH sensitivity of zK2P17.1 currents need to be considered when zebrafish data are extrapolated to human physiology.

Fully digital data processing during cardiovascular implantable electronic device follow-up in a high-volume tertiary center.

BACKGROUND: Increasing numbers of patients with cardiovascular implantable electronic devices (CIEDs) and limited follow-up capacities highlight unmet challenges in clinical electrophysiology. Integrated software (MediConnect®) enabling fully digital processing of device interrogation data has been commercially developed to facilitate follow-up visits. We sought to assess feasibility of fully digital data processing (FDDP) during ambulatory device follow-up in a high-volume tertiary hospital to provide guidance for future users of FDDP software. METHODS: A total of 391 patients (mean age, 70 years) presenting to the outpatient department for routine device follow-up were analyzed (pacemaker, 44%; implantable cardioverter defibrillator, 39%; cardiac resynchronization therapy device, 16%). RESULTS: Quality of data transfer and follow-up duration were compared between digital (n = 265) and manual processing of device data (n = 126). Digital data import was successful, complete and correct in 82% of cases when early software versions were used. When using the most recent software version the rate of successful digital data import increased to 100%. Software-based import of interrogation data was complete and without failure in 97% of cases. The mean duration of a follow-up visit did not differ between the two groups (digital 18.7 min vs. manual data transfer 18.2 min). CONCLUSIONS: FDDP software was successfully implemented into the ambulatory follow-up of patients with implanted pacemakers and defibrillators. Digital data import into electronic patient management software was feasible and supported the physician's workflow. The total duration of follow-up visits comprising technical device interrogation and clinical actions was not affected in the present tertiary center outpatient cohort.