Recording Fast Ion Channel Kinetics Using Non-invasive Electrical Impedance Spectroscopy

Abstract Ligand-gated ion channels are involved in numerous pathophysiological processes and are, therefore, important targets for drug discovery. We describe a new microfluidic lab-on-a-chip device that allows the recording of fast ligand-gated ion channel kinetics in Xenopus laevis oocytes by non-invasive electrical impedance spectroscopy (EIS). The device, designated as Aachen Fast Ion Channel Sensor (AFIS) system, consists of two chambers separated by an orifice for capturing an oocyte by applying suction to the lower chamber. For channel recordings, annular electrodes are placed above and below the orifice. As a proof of concept, we recorded the EIS responses of the X. laevis oocyte-expressed human P2X2 receptor (hP2X2R), which functions as a non-desensitizing adenosine triphosphate (ATP)-gated cation-selective channel. The impedance data were fitted with an appropriate equivalent electrical circuit model. After ATP application, both EIS and TEVC recordings showed similar fast responses, which reflected the rapid solution exchange. Concentration–response curves determined by EIS or TEVC were virtually similar, indicating that agonist potency can be reliably determined by EIS. The oocytes survived the EIS measurements intact and can be reused for further electrophysiological or other purposes. The AFIS system can be used with the noticeable electrical leakage between the oocyte and the orifice. This feature significantly reduces the amount of preparation time required to create a high-resistance seal. Therefore, the system offers the possibility to easy perform high-throughput drug screening, especially when multiple measurement sites are placed on one chip and a multiplexer is connected for simultaneous EIS measurements.