Alexandra Bussek

Adult human heart slices are a multicellular system suitable for electrophysiological and pharmacological studies.

Electrophysiological and pharmacological data from the human heart are limited due to the absence of simple but representative experimental model systems of human myocardium. The aim of this study was to establish and characterise adult human myocardial slices from small patients heart biopsies as a simple, reproducible and relevant preparation suitable for the study of human cardiac tissue at the multicellular level. Vibratome-cut myocardial slices were prepared from left ventricular biopsies obtained from end-stage heart failure patients undergoing heart transplant or ventricular assist device implantation, and from hearts of normal dogs. Multiple slices were prepared from each biopsy. Regular contractility was observed at a range of stimulation frequencies (0.1-2 Hz), and stable electrical activity, monitored using multi-electrode arrays (MEA), was maintained for at least 8 h from slice preparation. ATP/ADP and phosphocreatine/creatine ratios were comparable to intact organ values, and morphology and gap junction distribution were representative of native myocardium. MEA recordings showed that field potential duration (FPD) and conduction velocity (CV) in human and dog slices were similar to the values previously reported for papillary muscles, ventricular wedges and whole hearts. Longitudinal CV was significantly faster than transversal CV, with an anisotropic ratio of 3:1 for human and 2.3:1 for dog slices. Importantly, slices responded to the application of E-4031, chromanol and 4-aminopyridine, three potassium channel blockers known to affect action potential duration, with an increase in FPD. We conclude that viable myocardial slices with preserved structural, biochemical and electrophysiological properties can be prepared from adult human and canine heart biopsies and offer a novel preparation suitable for the study of heart failure and drug screening.

Tissue slices from adult mammalian hearts as a model for pharmacological drug testing.

Aim: Isolated papillary muscles and enzymatically dissociated myocytes of guinea-pig hearts are routinely used for experimental cardiac research. The aim of our study is to investigate adult mammalian ventricular slices as an alternative preparation. Method: Vibratome cut ventricular slices (350 μm thick) were examined histologically and with 2-photon microscopy for fibre orientation. Intracellular action potentials were recorded with conventional glass microelectrodes, extracellular potentials were measured with tungsten platinum electrodes and multi-electrode arrays (MEA). Results: Dominant direction of fibre orientation was absent in vertical and horizontal transmural slices, but was longitudinal in tangential slices. Control action potential duration (APD90, 169.9 ± 4 ms) and drug effects on this parameter were similar to papillary muscles. The L-type Ca-channel blocker nifedipine shortened APD90 with a half maximal effective concentration (EC50) of 4.5 μM. The IKr blocker E4031 and neuroleptic drug risperidone prolonged APD90 with EC50 values of 31 nM and 0.67 μM, respectively. Mapping field potentials on multi-electrode arrays showed uniform spread of excitation with a mean conduction velocity of 0.47 m ⋅ s-1. Conclusion: Slices from adult mammalian hearts could become a useful routine model for electrophysiological and pharmacological research.

Class I/B antiarrhythmic property of ranolazine, a novel antianginal agent, in dog and human cardiac preparations

The aim of this study was to investigate the cellular electrophysiological effects of ranolazine on action potential characteristics. The experiments were carried out in dog and human cardiac preparations using the conventional microelectrode technique. In dog Purkinje fibres ranolazine produced a concentration- and frequency-dependent depression of the maximum rate of depolarization (V(max)) while action potential duration (APD) was shortened. In dog and human right ventricular papillary muscle ranolazine exerted no significant effect on APD, while it produced, like mexiletine, use-dependent depression of V(max) with relatively fast onset and offset kinetics. In dog midmyocardial preparations the drug did not exert statistically significant effect on repolarization at 10 μM, although a tendency toward prolongation was observed at 20 μM. A moderate lengthening of APD(90) by ranolazine was noticed in canine atrial preparations obtained from dogs in sinus rhythm and in tachypacing induced remodelled preparations. Use-dependent depression of V(max) was more pronounced in atria from dogs in sinus rhythm than those in remodelled atria or in the ventricle. These findings indicate that ranolazine, in addition to its known late sodium current blocking effect, also depresses peak I(Na) with class I/B antiarrhythmic characteristics. Although peak I(Na) inhibition by ranolazine is stronger in the atria, it is also substantial (at fast stimulation frequencies) in ventricular preparations. Ranolazine also decreased the dispersion of ventricular repolarization (the difference in APD(90) values between Purkinje fibres and papillary muscles), which can contribute to the antiarrhythmic property of the drug.

Cardiac tissue slices with prolonged survival for in vitro drug safety screening

INTRODUCTIONnWe have recently introduced the use of mammalian cardiac tissue slices for in vitro drug testing purposes. Here we show how this method can be applied for long-term studies in safety pharmacology.nnnMETHODSnIn freshly prepared cardiac slices from guinea-pig or rat ventricle, extracellular field potentials (FP) and intracellular action potentials (AP) were recorded in response to electrical stimulation using the 4-channel heart slice screening system Synchroslice. To assess viability of the slices on consecutive days after preparation, drug effects on FP/AP parameters, like duration and latency, were monitored.nnnRESULTSnIn the presence of the potassium channel blocker E4031 (1 μM), FP and AP duration (FPD and APD) were significantly increased (FPD, 39.0%; APD, 28.1%) in guinea-pig ventricular slices. Similar changes were observed 24-28 h after slice preparation (FPD, 48.6%; APD, 25.4%). Furthermore, AP duration was reduced in the presence of the calcium channel blocker nifedipine (10 μM) on the day of preparation (40.5%) and 24-28 h later (38.7%). In contrast, in the presence of the potassium channel blocker 4-aminopyridine (30 mM) AP duration was prolonged 4.95 and 4.19-fold, 2-8 h and 24-28 h after preparation, respectively. Finally, FP propagation was repeatedly slowed down by the gap junction blocker carbenoxolone (30 μM), as revealed from FP onset latency increases observed on three consecutive days (2-8 h after preparation, 93.0%; 24-28 h, 76.8%, 48-56 h, 61.7%).nnnDISCUSSIONnFreshly isolated cardiac slices reproduced established physiological and pharmacological responses for more than 24 h after preparation. Thus, cardiac slices can be used for several days after preparation which makes them a robust model for electrophysiological studies. We propose that cardiac slices can become a versatile tool in heart research and risk assessment of drugs.

Field and action potential recordings in heart slices: correlation with established in vitro and in vivo models

BACKGROUND AND PURPOSE Action potential (AP) recordings in ex vivo heart preparations constitute an important component of the preclinical cardiac safety assessment according to the ICH S7B guideline. Most AP measurement models are sensitive, predictive and informative but suffer from a low throughput. Here, effects of selected anti‐arrhythmics (flecainide, quinidine, atenolol, sotalol, dofetilide, nifedipine, verapamil) on field/action potentials (FP/AP) of guinea pig and rabbit ventricular slices are presented and compared with data from established in vitro and in vivo models.