Data Acquisition

Adult murine cardiomyocytes were isolated and subjected to line-scan Ca²⁺ imaging as described previously (Xie et al., 2015; Huang et al., 2021; Zhang et al., 2021). For Ca²⁺ spark measurement, cardiomyocytes were preloaded with 5-μmol/L fluo-4 AM (Thermofisher) for 15 min and subjected to line-scan imaging at a speed of 400 lines/s on a Leica TCS SP8 confocal microscope with 40× magnification and a 1.3-NA oil immersion objective. The scan zoom was adjusted to fit the cells, and the scan line was along their long axis. The excitation for Fluo-4 was 488 nm, and emission was collected at 505–530 nm. Ca²⁺ spark detection and analysis were performed using either the traditional method (Cheng et al., 1999) or the algorithms described in the Results section.