Optical Mapping of Membrane Potentials

Cells were prepared similar to that for membrane potential measurement and treated with the membrane potential kit (F10488; Thermo Fisher Scientific). Optical mapping was performed using the MiCAM02 imaging system (BrainVision, Tokyo, Japan) combined with MyoPacer EP (IonOptix, Westwood, MA, United States), as reported previously (Nakanishi et al., 2019 (link)). Briefly, after loading the cells, the cultures were electrically stimulated using a bipolar electrode. For aligned pattern, pacing was performed parallel or perpendicular to the direction of arranged nanofibers, using the same pacing positions for random and flat patterns. The pacing rate ranged from 0.5 Hz to 2 Hz in a gradient. The whole procedure was performed at 37°C under atmospheric conditions. Optical imaging was performed using the BV_Ana software (BrainVision, Tokyo, Japan).