Abstract

An ex-vivo cardiac model able to accurately predict the benefits and side-effects of new treatments could reduce the large number of flawed treatments entering in vivo testing. We have previously shown that cardiac tissue slices are a promising experimental platform as they retain structural and functional properties of the native heart, while allowing control over interventions and straightforward observations. Porcine hearts share anatomical, physiological and electrical characteristics with human hearts and are readily available from veterinary laboratories and abattoirs. The aim of this study was therefore to establish an ex-vivo model of porcine myocardium using organotypic slices from easily accessible porcine hearts and assess their electrophysiological and calcium handling properties.

Vibratome-cut myocardial slices (300–350 μm thick) were prepared from the sub-epicardial region of the left ventricle of porcine hearts (by-product from porcine carcasses provided by the Pirbright Institute). Slices were point-stimulated at cycle lengths (CL) ranging from 500 ms to 4000 ms, and analysed using a multi-electrode array system. Conduction velocity (CV) and field potential duration (FPD), an index of action potential duration, were measured. Ca2 +cycling was assessed using Fluo-4 AM and optical mapping, during field-stimulation at 500–4000 ms CL. Ca2 +transient duration at 50% recovery (CaTD50) and 75% recovery (CaTD75) were measured at each pacing CL. Data was analysed using one-way ANOVA and presented as mean ± SEM.

CV was 46 ± 10 cm/s along muscle fibre orientation and 14 ± 1 cm/s perpendicular to fibre orientation, with an anisotropic ratio of 3:1 (n=4 slices). Mean FPD was 316 ± 11 ms at 1000 ms CL (n=5 slices), similar to previously reported data using ventricular wedges. All slices displayed FPD restitution, with FPD prolongation at longer pacing cycle lengths (CL 500 ms: 239 ± 6 ms; CL 1500 ms: 351 ± 21 ms; CL 2000 ms: 367 ± 14 ms; CL 4000 ms: 412 ± 13 ms; n=4–5, ANOVA p<0.0001). CaTD50 and CaTD75 were significantly prolonged at longer pacing cycle lengths, indicating Ca2 +transient duration restitution properties (figure 1; n=5, ANOVA p=0.0004 and p<0.0001 for CaTD50 and CaTD75, respectively).

Our results show that myocardial slices prepared from porcine hearts maintain electrical and calcium cycling properties of the native myocardium and provide a novel ex-vivo multicellular preparation with potential applications in cardiac preclinical research.