Fig. 8. Images of spontaneous Ca²⁺ release in HEK293 cells expressing RyR3. (Aa) Sequence of seven confocal Ca²⁺ images of fluo-4 fluorescence in HEK293 cells expressing RyR3. The images in Aa were obtained at the time indicated by dashed vertical lines in Ab. (Ab) F and F₀ are fluorescence intensity at a certain time and at resting conditions, respectively. F/F₀ in circular spots (2 µm in diameter) at the point indicated by x, y and z, and that over the whole image of the part of the cell were measured and plotted against time. The black line indicates the change in F/F₀ over the whole area of the cell. Bar in panel Aa, 10 µm. (B) Images of Ca²⁺ sparks (a) and F/F₀ in the areas x, y and z in the same cell.