Influence of the first amplifier stage in MEA systems on extracellular signal shapes

Recording of extracellular signals with planar metal microelectrodes (ME) has already been presented more than 30 years ago. To date, microelectrode array (MEA) systems are able to measure extracellular signals at about 64 sites, simultaneously. This enables monitoring of electrical activity of many cells in a large area. The extracellular recording technique has become a widely used method for neurological, toxicological or pharmacological studies. It already proved its potential to supplement the classical methods in electrophysiology. The interpretation of the recorded signal shapes in order to extract electrophysiological meaningful data--however--is still under discussion. In this article, we analyse the preamplifier circuit for extracellular recording of cardiac myocyte signals. We use a circuit model for the cell-electrode contact including the first amplification stage. In test experiments, we observe different signal shapes, when different shunt resistors are introduced at the input of the preamplifier. According to the frequency spectra of the recordings, we evaluate the transfer function between the source signal and the readout signal. As a result of our studies, an optimum readout electronics for originally, preserved extracellular signal shapes is proposed. Our amplifier design will be most valuable, if the use of small microelectrodes with high input impedances for in vitro as well as for in vivo experiments is desired.