DiscussionHamamatsu has developed a 96-channel electrode array system that is mounted on the FDSS/μCELL. It adds electric field stimulations (EFS) to all 96 wells in a microplate simultaneously while fluorescence/luminescence signals are monitored. We measured oscillations of intracellular Ca2+ concentration, which occurs along with the beating of the cells, with a calcium sensitive fluorescent dye in mouse ESC-derived cardiomyocytes (Cor.At®,Axiogenesis). We observed that the Ca2+ oscillation was synchronized to the electric stimulation, which indicates that the EFS system is able to pace the beatings of cardiomyocytes. In the presence of some ion channel blockers, EFS was added at various frequencies to see frequency-dependent responses. Such intracellular Ca2+ kinetics measurements coupled with electric stimulation would be useful in the assessment of cardiac toxicity of pharmacological compounds, in particular in the toxicity screening at the early stages of drug development.