After ELF-EMF exposure for 3 days, the cells were loaded with HEPES-buffered salt solution (HBSS) containing Fura 2-AM (5 μM, Dojindo, Japan) and 0.01% pluronic acid-127 (Sigma-Aldrich, USA) for 45 min at 37°C and then incubated in fresh HBSS for another 30 min to allow deesterification of the Fura-2 AM. Next, the cells were exposed to the 1 mT ELF-EMF for 30 min, and then the intracellular calcium was immediately measured using an Infinite M200 Microplate Reader (TECAN, Austria).