Comparison of Functional Parameter Measured from Tissues Slices and Whole-Heart

Abstract

Cardiac tissue slices, pseudo 2D preparations of heart muscle, form a very promising candidate to study patho-physiological mechanisms underlying cardiac behaviour. However, little is known about how slice and intact whole-heart action-potential (AP) properties are interrelated, and how to scale-up from observations in ‘2D' to the 3D heart. Here, we compare AP properties of intact whole-heart and slices.Langendorff-perfused guinea-pig (female, 300-400g) whole hearts were loaded with voltage-sensitive dye Di-4-ANBDQPQ (15μL, 19mg/mL in Ethanol). The AP was optically mapped (Cascade128+, ∼500Hz) using blue excitation light (LED-CBT90 Luminus, filter: HQ460/80M) to maximise signal collection from surface/subsurface layers of the left ventricle (LV). While hearts were perfused (Krebs buffer), thin (400μm) tissue slices were cut tangentially to the mapped epicardial surface using a high-precision microtome (7000smz, Campden). Slices and freshly exposed surface were optically mapped while paced at frequencies from 1 to 5 Hz. This was repeated until the LV wall was completely sectioned.Our data so far show that the average AP duration at 80% repolarisation (APD80) measured from Langendorff-perfused heart LV epicaridal/subepicardial tissue at 4Hz was 123.8 (±1.6)ms, while in 2D epicaridal slices it was 124.5 (±1.2)ms. Normalised area under AP curve, an indicator for AP shape, was 0.706(±0.010) in 3D-heart epicardium/subepicardium, and 0.705(±0.005) in 2D-slices. Although slices differ from whole-hearts in terms of electrical source-sink relations and mechanical load, APD and AP-shape ranges were not dissimilar (t-test, 95% significance-level). This suggests that tissue slices preserve some of the key AP-characteristics relevant for the study of mechanisms underlying cardiac patho-physiology.