Abstract
Introduction: Cardiac tissue slices, a pseudo two-dimensional organo-typic experimental model, are an increasingly popular model to study cardiac biophysics in-vitro. This preparation benefits from moderate complexity, native cell-type presence, and locally preserved cell-cell connections. We used optical mapping of tissue slices to monitor transmembrane potential (Vm) and intracellular Ca2+ concentration to study the effects of stretch on action potential duration (APD) and calcium transient (CaT) dynamics with a relatively high spatio-temporal resolution, to explore mechanisms of stretch-induced arrhythmias.Methods: Langendorff perfused rabbit hearts were loaded with dyes for Vm (di-4-ANBDQPQ) and CaT (Rhod-2-AM). Thereafter, 350 µm tissue slices were vibratome-cut from left and right ventricular free wall in an epicardium-tangential plane. Slices were attached at their ends to a manual stretcher and optically mapped using an EMCCD camera with LED excitation light sources. Slices were field stimulated at 2Hz, and Vm and CaT were measured before, during (up to 50min) and after application of stretch.Results: Cardiac tissue slices (n=9), exposed to stretch (by 4-12%) showed an initial shortening in both APD and CaT duration (APD80 and APD50 reduced by 10.7% and 11.4%, respectively; CaT80 and CaT50 reduced by 6% and 5.3%, respectively). During maintained stretch, a gradual re-lengthening of APD and CaT duration was observed. After release of stretch, APD and CaT duration reverted to shorter values.Conclusion: Living cardiac tissue slices offer a promising experimental model for the study of cardiac mechano-electric coupling. The methodology described can be refined (e.g. using a computer-controlled motorised stage to synchronise electrical and mechanical events, and by use of fiducial markers to track local tissue deformation rather than only input strain levels) and extended (e.g. exploring effects of stretch directionality, relative to prevailing cell orientation in a slice).
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