Validation of Electrical Signaling in In Vitro Cell Cultures on Multielectrode Arrays through Simultaneous Calcium Imaging

The in vitro measurement of electrical activity from networks of neurons requires a high spatial as well as temporal resolution. There are multiple different technologies that can be used to record these signals from a variety of different cell cultures such as cardiac myocytes, primary neurons and organotypic slices, the most prominent of which are multielectrode arrays (MEAs) and calcium imaging (CI). MEA systems are able to measure extracellular potential changes of cells near the electrodes on their surface. Recorded signals have a high temporal resolution in the sub-millisecond range, but the spatial resolution is limited by the distance between the recording electrodes. In CI, the cell culture is loaded with calcium sensitive dyes to detect changes in the intra- and extracellular calcium concentrations with fluorescence microscopy, which is an indicator for electrical activity. The resulting microscope recordings provide a high spatial resolution, but the temporal resolution is limited by the slow calcium transients lasting up to several hundred milliseconds. Some CI modalities may even be used to measure subthreshold membrane potentials, which cannot be detected with extracellular MEA recordings. Here, we combine these two methods and correlate the recorded signals to generate data with a highly optimized spatial and temporal resolution. Furthermore, MEAs can be used to electrically stimulate cell cultures to distinguish electrically active cells from unexcitable cells, such as astrocytes, in a simultaneous recording.