Action potential propagation failures in long-term recordings from embryonic stem cell-derived cardiomyocytes in tissue culture

Three-dimensional cell aggregates (embryoid bodies, EBs) containing cluster s of spontaneously beating cardiomyocytes were derived from permanent mouse embryonic stem (ES) cells. Extracellular recordings of the population acti on potentials of cardiomyocyte clusters were made using permanently mounted silver wire electrodes and microelectrode arrays integrated into the botto m of the culture dish. These techniques allowed long-term recordings (for u p to several weeks) from individual EBs under cell culture conditions. The normal electrical activity consisted of regular spiking with a frequency of 0.5-5 Hz. However, most EBs (87%) spontaneously developed temporary or per sistent complex activity patterns because of intermittent block of action p otential propagation at narrow pathways connecting larger beating areas. Si milar propagation blocks could also be reversibly induced in regularly spik ing EBs by nimodipine (NDP). In addition to a slowing of pacemaker activity , NDP (20-200 nM) induced a stepwise decrease of the action potential frequ ency at the recording site. Perforated patch-clamp recordings from enzymati cally isolated ES-cell-derived cardiomyocytes showed that similar activity patterns do not occur at the single-cell level. We suggest that this novel approach may provide a useful tool for in vitro studies of chronotropy and phenomena of propagation failure similar to AV block.