Fig. 4: Performances of NEMOer sensors in monitoring sarcoplasmic reticulum (SR) Ca²⁺ dynamics in cardiomyocytes.

A SR load measurement by 30 mM caffeine perfusion in neonatal rat cardiomyocytes. Top, pseudocolor image showing a typical cell expressing NEMOer-f; bottom, averaged time curves showing caffeine-induced responses of transiently expressed indicators. The arrow indicates the time of caffeine stimulation. Scale bar, 10 μm. Typical figure captured from 6 cells across 75 one-day-old Sprague-Dawley rats in three independent experiments, showing consistent reproducibility across experiments. B Subcellular distribution of NEMOer-f fluorescence in adult rat cardiomyocyte revealed with confocal imaging. Top left, typical confocal images; top right, enlarged view of boxed area shown in top left image; bottom trace, spatial profile for the boxed region. Typical figure captured from 15 cells across 3 adult rats in three independent experiments, showing consistent reproducibility across experiments. C–E Local and global cytosolic and SR Ca²⁺ dynamics in adult rat cardiac myocytes revealed by dual-color imaging using NEMOer-f and a cytosolic Ca²⁺ indicator, Rhod-2. Top, typical line-scan images; bottom, corresponding mean time course plots. Ca²⁺ responses induced by caffeine (30 mM) (C). Local SR Ca²⁺ scraps and accompanying cytosolic Ca²⁺ transient are triggered by electric field stimulation (D) or during a spontaneous release (E), either under control (CT) (left) or when treated with 100 nM norepinephrine (NE) (right). (C, n = 6 cells; D, n = 14 cells; E left trace, n = 11 cells; (E) right trace, n = 20 cells. Data from 3 adult rats). Data is shown as mean ± s.e.m. F Spontaneous elementary cytosolic Ca²⁺ spark and SR Ca²⁺ blink events under CT (left) or NE-treated (right) conditions revealed by Rhod-2 and NEMOer-f, respectively. Typical line-scan images are shown on the left; corresponding time-course curves are shown on the right.