Microelectrode arrays: a new tool to measure embryonic heart activity.

The analysis of the sequential excitation of cardiac tissue is of high relevance, both for clinical pathophysiological purposes, eg, detection of sustained ventricular arrhythmias, as well as for experimental electrophysiology. Clinically, different technical approaches such as single electrode measurements and bipolar mapping electrode catheters have been used. In experimental setups several techniques to record cardiac activity have been proposed. Beside the well-established intracellular current-clamp recordings of action potentials, recent studies have performed extracellularly activation sequence mapping or simultaneous multichannel action potential electrode array measurements. Measurement of extracellularly recorded field potentials (FPs) hereby especially provides detailed information about the origin and spread of excitation in the heart. A similar analytical approach for cardiac FPs advanced the analysis of excitation spread and arrhythmic activity in multicellular preparations like developmental differentiation tissue of mouse embryonic stem cells, multicellular preparations of isolated native embryonic cardiomyocytes or the embryonic heart in toto. The use of substrate-integrated Microelectrode Arrays (MEAs, Multi Channel Systems, Reutlingen, Germany) with 60 electrodes of 10-30 microm diameters on a 100-200 microm grid, coated with porous titanium nitride to minimize the impedance allows recording of FPs at a high signal to noise ratio. The possibility to electrically stimulate the tissue further expands the range of applications and bioassays. It may thus facilitate the evaluation of drug research providing detailed information about the interplay of the complex cardiac network, and might improve the predictability of physiological and pathophysiological conditions or drug effects in embryonic heart tissue.