We used previous data [8 (link)] acquired as briefly described below. An inverted microscope (IX-70, Olympus) was equipped with a high-sensitivity camera (iXon 3 860, iXon Ultra, Andor Technology) and an oil-immersed objective lens (UPlanSapo 100 XO, Olympus). The pixel size of the camera corresponded to the cell length of 150 nm, and a frame rate of 500 fps was used for high-resolution temporal analysis. The temperature of the glass slide seeded with cardiomyocytes was maintained at (37.0±0.2)°C using a thermostat-controlled incubator (INUG 2-ONICS, Tokai Hit) on the sample stage. A 1550 nm laser (FPL 1055 T, Thorlabs) was used as a heat source to rapidly change the temperature near the cardiomyocytes to be monitored. HSOs were induced by application of heat in the vicinity of cardiomyocytes. A 488 nm laser (FITEL HPU50211, Furukawa Electric Co., Ltd.) was used as an excitation light source for observing the fluorescence of AcGFP-α-actinin.
The observation of HSOs with simultaneous measurement of changes in Fluo4 fluorescence intensity used previous data [7 (link)]. In this observation, HSOs were observed in cases where there was a change in intracellular calcium concentration (HSOs with beating) and when the intracellular calcium concentration was maintained constant in the same manner as during Cell-SPOCs observation (HSOs without beating).
The observation of HSOs with simultaneous measurement of changes in Fluo4 fluorescence intensity used previous data [7 (link)]. In this observation, HSOs were observed in cases where there was a change in intracellular calcium concentration (HSOs with beating) and when the intracellular calcium concentration was maintained constant in the same manner as during Cell-SPOCs observation (HSOs without beating).
