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

INTRODUCTION: We 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.
METHODS: In 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.
RESULTS: In 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%). DISCUSSION: Freshly 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.