Determination of electrical properties of ES cell-derived cardiomyocytes using MEAs

Pluripotent embryonic stem cells (ES cells) provide a novel tool to study cardiomyogenesis under in vitro conditions. This overview article focuses on the technical properties of extracellular recordings of ES cell-derived cardiomyocytes using Microelectrode Arrays (MEAs). It reviews recent experimental observations, in an effort to describe basic characteristics of field potentials (FPs) in the ES cell model of developing myocardium. ES cells kept in permanent culture are differentiated within aggregates ("embryoid bodies", EBs) in which among other cell types cardiomyocytes appear 3-4 days after plating. These form spontaneously beating clusters mostly consisting of expanded regions of cardiac cells connected with narrow tissue strands. To record the electrical activity of these contracting areas substrate-integrated MEAs consisting of 60 substrate-integrated electrodes can be used. We previously investigated the influence of Na+-, K+- and Ca2+ channel blockers on the electrical signal generation and propagation as well as on the shape of FPs. We also used ES cell-derived cardiac myocytes as a multicellular in vitro model for cardiac development. Long-term recordings with a MEA enabled the examination of electrophysiological properties during the ongoing differentiation process. During time in culture the beating aggregate of cardiac myocytes differentiating from ES cells increased in size (7-fold). This change was accompanied by an increase of the beating frequency from 1 to 5 Hz and a decrease of the FP duration. Furthermore a shortening of the FP upstroke velocity could be observed concomitant with a functional segregation of slow upstroke velocities in the area of the pacemaker. Our data indicate a functional differentiation and segregation of the cells into pacemaker and myocard-like regions. This in vitro development of a three-dimensional heart like structure closely follows the development known from mouse embryonic heart. The preparation thus forms an ideal model to monitor the development of electrical activity in embryonic cardiac myocytes for wild type and genetically modified ES cells, thereby taking into account the functional differentiation of the tissue. Our data suggest that EBs plated on MEAs provide a suitable tool for pre-screening of cardioactive substances.