*These two authors contributed equally to this work. †These two senior authors contributed equally to this work. BACKGROUND AND PURPOSEThe reliable assessment of proarrhythmic risk of compounds under development remains an elusive goal. Current safety guidelines focus on the effects of blocking the KCNH2/HERG ion channel-in tissues and animals with intact repolarization. Novel models with better predictive value are needed that more closely reflect the conditions in patients with cardiac remodelling and reduced repolarization reserve. EXPERIMENTAL APPROACHWe have developed a model for the long QT syndrome type-5 in rabbits (LQT5 ) with cardiac-specific overexpression of a mutant (G52R) KCNE1 β-subunit of the channel that carries the slow delayed-rectifier K + -current (I Ks ). ECG parameters, including short-term variability of the QT interval (STV QT ), a biomarker for proarrhythmic risk, and arrhythmia development were recorded. In vivo, arrhythmia susceptibility was evaluated by i.v. administration of the I Kr blocker dofetilide. K + currents were measured with the patch-clamp technique. KEY RESULTSPatch-clamp studies in ventricular myocytes isolated from LQT5 rabbits revealed accelerated I Ks and I Kr deactivation kinetics. At baseline, LQT5 animals exhibited slightly but significantly prolonged heart-rate corrected QT index (QTi) and increased STV QT . Dofetilide provoked Torsade-de-Pointes arrhythmia in a greater proportion of LQT5 rabbits, paralleled by a further increase in STV QT . CONCLUSION AND IMPLICATIONSWe have created a novel transgenic LQT5 rabbit model with increased susceptibility to drug-induced arrhythmias that may represent a useful model for testing proarrhythmic potential and for investigations of the mechanisms underlying arrhythmias and sudden cardiac death due to repolarization disturbances. AbbreviationsHERG, human ether-a-go-go gene; I Ca,L , L-type Ca 2+ current; I K1 , inward rectifier potassium current; I Kr , rapid delayed rectifier potassium current; I Ks , slow delayed rectifier potassium current; I to , transient outward potassium current; KCNE1, potassium voltage-gated channel subfamily E member 1; LQT5, long QT syndrome type 5; minK, minimum sequence required for a potassium current; QTi, heart rate-corrected QT index; STV QT , short-term variability of the QT interval; STV RR , short-term variability of the RR interval; TdP, Torsade-de-Pointes; TG, transgenic; WT, wild type

BACKGROUND AND PURPOSEAtrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with an increased risk for stroke, heart failure and cardiovascular-related mortality. Candidate targets for anti-AF drugs include a potassium channel Kv1.5, and the ionic currents IKACh and late INa, along with increased oxidative stress and activation of NFAT-mediated gene transcription. As pharmacological management of AF is currently suboptimal, we have designed and characterized a multifunctional small molecule, compound 1 (C1), to target these ion channels and pathways. EXPERIMENTAL APPROACHWe made whole-cell patch-clamp recordings of recombinant ion channels, human atrial IKur, rat atrial IKACh, cellular recordings of contractility and calcium transient measurements in tsA201 cells, human atrial samples and rat myocytes. We also used a model of inducible AF in dogs. KEY RESULTSC1 inhibited human peak and late Kv1.5 currents, frequency-dependently, with IC50 of 0.36 and 0.11 μmol·L −1 respectively. C1 inhibited IKACh (IC50 of 1.9 μmol·L −1 ) and the Nav1.5 sodium channel current (IC50s of 3 and 1 μmol·L −1 for peak and late components respectively). C1 (1 μmol·L −1 ) significantly delayed contractile and calcium dysfunction in rat ventricular myocytes treated with 3 nmol·L −1 sea anemone toxin (ATX-II). C1 weakly inhibited the hERG channel and maintained antioxidant and NFAT-inhibitory properties comparable to the parent molecule, resveratrol. In a model of inducible AF in conscious dogs, C1 (1 mg·kg −1 ) reduced the average and total AF duration. CONCLUSION AND IMPLICATIONSC1 behaved as a promising multifunctional small molecule targeting a number of key pathways involved in AF. AbbreviationsAERP, atrial effective refractory period; AF, atrial fibrillation; BCL, basic cycle length; CABG, coronary artery bypass graft surgery; C1, compound 1; DPPH, diphenylpicrylhydrazyl; NRVM, neonatal rat ventricular myocytes BJP British Journal of Pharmacology

BackgroundThe aim of the present work was to characterize the electrophysiological effects of the non-steroidal anti-inflammatory drug diclofenac and to study the possible proarrhythmic potency of the drug in ventricular muscle.MethodsIon currents were recorded using voltage clamp technique in canine single ventricular cells and action potentials were obtained from canine ventricular preparations using microelectrodes. The proarrhythmic potency of the drug was investigated in an anaesthetized rabbit proarrhythmia model.ResultsAction potentials were slightly lengthened in ventricular muscle but were shortened in Purkinje fibers by diclofenac (20 µM). The maximum upstroke velocity was decreased in both preparations. Larger repolarization prolongation was observed when repolarization reserve was impaired by previous BaCl2 application. Diclofenac (3 mg/kg) did not prolong while dofetilide (25 µg/kg) significantly lengthened the QTc interval in anaesthetized rabbits. The addition of diclofenac following reduction of repolarization reserve by dofetilide further prolonged QTc. Diclofenac alone did not induce Torsades de Pointes ventricular tachycardia (TdP) while TdP incidence following dofetilide was 20%. However, the combination of diclofenac and dofetilide significantly increased TdP incidence (62%). In single ventricular cells diclofenac (30 µM) decreased the amplitude of rapid (IKr) and slow (IKs) delayed rectifier currents thereby attenuating repolarization reserve. L-type calcium current (ICa) was slightly diminished, but the transient outward (Ito) and inward rectifier (IK1) potassium currents were not influenced.ConclusionsDiclofenac at therapeutic concentrations and even at high dose does not prolong repolarization markedly and does not increase the risk of arrhythmia in normal heart. However, high dose diclofenac treatment may lengthen repolarization and enhance proarrhythmic risk in hearts with reduced repolarization reserve.

Significant reduction of concentration of some pesticide residues and substantial increase of the uncertainty of the results derived from the homogenization of sample materials have been reported in scientific papers long ago. Nevertheless, performance of methods is frequently evaluated on the basis of only recovery tests, which exclude sample processing. We studied the effect of sample processing on accuracy and uncertainty of the measured residue values with lettuce, tomato, and maize grain samples applying mixtures of selected pesticides. The results indicate that the method is simple and robust and applicable in any pesticide residue laboratory. The analytes remaining in the final extract are influenced by their physical-chemical properties, the nature of the sample material, the temperature of comminution of sample, and the mass of test portion extracted. Consequently, validation protocols should include testing the effect of sample processing, and the performance of the complete method should be regularly checked within internal quality control.

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. It can occur at any age, however, it becomes extremely common in the elderly, with a prevalence approaching more than 20% in patients older than 85 years. AF is associated with a wide range of cardiac and extra-cardiac complications and thereby contributes significantly to morbidity and mortality. Present therapeutic approaches to AF have major limitations, which have inspired substantial efforts to improve our understanding of the mechanisms underlying AF, with the premise that improved knowledge will lead to innovative and improved therapeutic approaches. Our understanding of AF pathophysiology has advanced significantly over the past 10 to 15 years through an increased awareness of the role of "atrial remodeling". Any persistent change in atrial structure or function constitutes atrial remodeling. Both rapid ectopic firing and reentry can maintain AF. Atrial remodeling has the potential to increase the likelihood of ectopic or reentrant activity through a multitude of potential mechanisms. The present paper reviews the main novel results on atrial tachycardia-induced electrical, structural and contractile remodeling focusing on the underlying pathophysiological and molecular basis of their occurrence. Special attention is paid to novel strategies and targets with therapeutic significance for atrial fibrillation.