Living cardiac tissue slices: An organotypic pseudo two-dimensional model for cardiac biophysics research

Abstract

Living cardiac tissue slices, a pseudo two-dimensional (2D) preparation, have received less attention than isolated single cells, cell cultures, or Langendorff-perfused hearts in cardiac biophysics research. This is, in part, due to difficulties associated with sectioning cardiac tissue to obtain live slices. With moderate complexity, native cell-types, and well-preserved cell-cell electrical and mechanical interconnections, cardiac tissue slices have several advantages for studying cardiac electrophysiology. The trans-membrane potential (Vm) has, thus far, mainly been explored using multi-electrode arrays. Here, we combine tissue slices with optical mapping to monitor Vm and intracellular Ca(2+) concentration ([Ca(2+)]i). This combination opens up the possibility of studying the effects of experimental interventions upon action potential (AP) and calcium transient (CaT) dynamics in 2D, and with relatively high spatio-temporal resolution. As an intervention, we conducted proof-of-principle application of stretch. Mechanical stimulation of cardiac preparations is well-established for membrane patches, single cells and whole heart preparations. For cardiac tissue slices, it is possible to apply stretch perpendicular or parallel to the dominant orientation of cells, while keeping the preparation in a constant focal plane for fluorescent imaging of in-slice functional dynamics. Slice-to-slice comparison furthermore allows one to assess transmural differences in ventricular tissue responses to mechanical challenges. We developed and tested application of axial stretch to cardiac tissue slices, using a manually-controlled stretching device, and recorded Vm and [Ca(2+)]i by optical mapping before, during, and after application of stretch. Living cardiac tissue slices, exposed to axial stretch, show an initial shortening in both AP and CaT duration upon stretch application, followed in most cases by a gradual prolongation of AP and CaT duration during stretch maintained for up to 50 min. After release of sustained stretch, AP duration (APD) and CaT duration reverted to shorter values. Living cardiac tissue slices are a promising experimental model for the study of cardiac mechano-electric interactions. The methodology described here can be refined to achieve more accurate control over stretch amplitude and timing (e.g. using a computer-controlled motorised stage, or by synchronising electrical and mechanical events) and through monitoring of regional tissue deformation (e.g. by adding motion tracking).

Comparing maximum rate and sustainability of pacing by mechanical vs. electrical stimulation in the Langendorff-perfused rabbit heart

“…To determine the relative contributions of potential mechanisms (altered ion channel activity, ionic concentrations, intracellular or sarcolemmal domains and tissue mechanics) experiments should involve: (i) pharmacological modulation of relevant ion fluxes and/or sub-cellular structures; (ii) domain-specific modulation or reporting of changes in ion concentrations and/or buffering; (iii) alteration of extracellular biophysical properties, from composition of solutions to background ventricular pressure/volume load or material stiffness (cytoskeletal disruption and cross-bridge inhibition); and (iv) variation of MS characteristics (indentation magnitude and rate, force and contact area/pressure under the probe), combined with measurement of strain and force (preliminary results have shown an inter-dependence of VE M on indentation magnitude and rate, Figure 7 ) to assess, for example, whether MS at the point of failed 1:1 capture may still initiate VE M if using higher mechanical stimulus intensities (‘relative refractoriness’). Additional key experiments involve work at various levels of structural integration, for example to determine maximum rates and sustainability of MS and ES in single isolated cardiomyocytes, or of the effects of non-myocytes 40 on cardiomyocyte responses to MS and ES in cell culture 41 or tissue slices, 42 combined with quantitative computational integration of findings 43 . Of further interest would be investigations into various pathophysiological states to determine the influence of disease background, and in multiple species, to test for conservation of effects.…”

Excitation-Contraction Coupling in Zebrafish Ventricular Myocardium Is Regulated by Trans-Sarcolemmal Ca2+ Influx and Sarcoplasmic Reticulum Ca2+ Release

“…Due to the simplicity of the preparation and experimental approach, heart slices have become a popular technique especially in the recent years and have been prepared from many mammalian species [ 16 ]. While a zebrafish whole-heart preparation is relatively straightforward compared to mammalian whole-heart preparations and can even be maintained in culture up to three days in vitro [ 17 ], heart slices are particularly suitable for isometric force measurements of ventricular working myocardium [ 14 ].…”

Myocyte-fibroblast communication in cardiac fibrosis and arrhythmias: Mechanisms and model systems

“…Slices of living cardiac tissue from humans and animal models are also being proposed as an experimental model system to better understand cell-cell communication in the context of the diseased heart [131–133]. This experimental system presents some advantages in that it is (i) directly relevant to humans, (ii) provides an environment that retains the native cytoarchitecture of myocyte-fibroblast interactions in the context of disease and (iii) can be exploited for pharmacological drug screening.…”