Introduction: Organotypic cardiac slices as models for testing physiological and pharmacological interventions are recognised to offer unique advantages over whole perfused organs or single isolated cardiomyocytes for several reasons. To name just a few, slices allow multiple experimental samples from biopsies; they can be maintained under culture conditions for several days; they consist of mature cells; and multicellularity and intercellular contacts as well as ECM are preserved. Thus, they provide a promising approach for short- and long-term drug screening. Our aim is to validate the model by testing the electrophysiological effects of standard antiarrhythmic drugs: flecainide (class 1c antiarrhythmic) and dofetilide (class 3 antiarrhythmic) in slices of human hearts.
Methods: Cardiac tissue excised from patients was sliced into 400 µm thick sections, mounted in biomimetic chambers (MyoDish), and paced electrically at a frequency of 1 Hz. A preload of 1 mN was applied. Action potentials (AP) were recorded at 37°C using sharp intracellular microelectrodes pulled from borosilicate glass capillaries (tip resistance 15-20 MΩ when filled with 3 M KCl solution). The bath solution contained (in mM): NaCl 140, KCl 5.4, HEPES 10, CaCl2 1.8, MgCl2 1, glucose 10. Observations before, during and after drug interventions are all paired. All values are reported as mean ± standard deviation.
Results: AP from left ventricular slices had resting membrane potentials (RMP) of -83.7 ± 5.5 mV, AP amplitudes (APA) of 110.4 ± 7.1 mV, maximal depolarization speeds (dV/dtmax) of 104.3 ± 45.7 mV/ms, AP durations at 30% of repolarization (APD30) of 214.6 ± 24.0 ms, APD50 of 327.2 ± 58.1 ms and APD90 of 460.1 ± 72.4 ms (N=8 hearts, n=18 slices). The APD90/APD50 and APD90/APD30 ratios were 1.42 ± 0.07 and 2.17 ± 0.26, respectively. Thus, AP exhibited consistent shapes during phase 3 though the APD50 and APD90 values varied considerably among patients. Flecainide caused a reversible decrease in dV/dtmax of 25.8 ± 13.2% at 3 µM (N=3, n=6) while APD90 was not significantly altered. Dofetilide reversibly increased APD90 by 22.2 ± 3.2% at 10 nM, and by 50.1 ± 3.9% at 30 nM (N=1, n=2).
Conclusion: The organotypic cardiac slice model produced consistent results with regard to RMP and APA values, and AP shape showed clear triangularisation. Although other AP parameters, such as dV/dtmax and individual APD varied among patients, known antiarrhythmic drugs tested produced the expected effects. The results obtained in this study suggest that the slice model is suitable for testing of drug effects on key parameters of cardiac electrophysiology, making this model promising for assessing novel antiarrhythmic drugs.
