Cardiac Tissue Slices: Preparation‚ Handling‚ and Successful Optical Mapping

Abstract

Cardiac tissue slices are becoming increasingly popular as a model system for cardiac electrophysiology and pharmacology research and development. Here, we describe in detail preparation, handling and optical mapping of trans-membrane potential and intracellular free calcium concentration transients (CaT) in ventricular tissue slices from guinea pigs and rabbits. Slices cut in the epicardium-tangential plane contained well-aligned in-slice myocardial cell strands ('fibres') in sub-epicardial and mid-myocardial sections. Cut with a high-precision slow-advancing microtome at a thickness of 350 to 400 μm, tissue slices preserved essential AP properties of the pre-cutting Langendorff perfused heart. We identified the need for a post-cutting recovery period of 36 min (guinea pig) and 63 min (rabbit) to reach 97.5% of final steady-state values for action potential (AP) duration (APD) (identified by exponential fitting). There was no significant difference between the post-cutting recovery dynamics in slices obtained using 2,3-butanedione 2-monoxime or blebistatin as electro-mechanical uncouplers during the cutting process. The rapid increase in APD after cutting was mainly caused by the exposure to ice-cold solution during the slicing procedure, not by tissue injury, differences in uncouplers, or pH-buffers (bicarbonate; HEPES) used. To characterise intrinsic patterns of CaT, AP, and conduction, a combination of multi-point and field stimulation should be used to avoid misinterpretations based on source-sink effects. In summary: we describe in detail the preparation, mapping, and data analysis approaches for reproducible cardiac tissue slice-based investigations into AP and CaT dynamics.