Implementation of an electric cell-substrate impedance sensing (ECIS) protocol to parametrize 2D induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) cultures

Abstract

The ECIS technique was developed to investigate the barrier function of confluent epithelial and endothelial cells by measuring the impedance of cell cultures in a wide range of frequencies. The physical interpretation of the data is based on equivalent circuit models. One model developed by Giaever and Keese (1991, GK model) assumes that confluent cells interact with each other and the substrate creating two defined resistances: Rb, the resistance of the space between cells and a, the resistance space occupied by the substrate between the cell and the electrode. The model also includes the cell membrane capacitance (Cm). The goal of this research was 1) to establish whether cardiomyocyte phenotypes can be defined by the strength of interaction between cells (Rb), the strength of interaction with the substrate (a), and the amount of cell membrane (Cm), and 2) whether these parameters define the electrophysiological properties of the 2D culture. Four iPSC-CM lines derived from healthy donors were differentiated using current protocols and transferred (100,000 cells/well) to 0.6 mm electrode CardioExcyte96 plates. The CardioExcyte96 was used to record extracellular field potentials and the AtlaZ was used to measure impedance values in the 0.1 to 100 kHz range. The GK model was fitted using an R script. The impedance measured at 10 kHz growth after cardiomyocyte plating, following a single exponential function stabilizing after 7 days. The normalized spectrum of the four cell lines showed a peak between 15 and 25 kHz. Rb ranged from 1.8 to 9.3 Wcm², a ranged from 5.1 to 7.4 W^0.5 cm and Cm ranged from 0.74 to 1.82 mFcm⁻². Rb was the most discriminative parameter between phenotypes and correlated with the Sodium Spike Amplitude but not with Field Potential duration or Beating Rate. This study suggests that ECIS parameters, particularly Rb, can differentiate cardiomyocyte phenotypes based on the strength of cell-cell interactions. This finding underscores the potential utility of ECIS in characterizing cellular behavior and electrophysiological properties in cardiomyocyte cultures for disease modeling and drug discovery.