Figure 1.

Relationship between Ca²⁺ sparks and their corresponding STOCs. The cells were voltage clamped at 0 mV, and the images were acquired at 333 Hz with an exposure time of 3 ms. Cytosolic Ca²⁺ was measured using 50 µM fluo-3, which was introduced into the cells in the K⁺ form through the patch pipette. (A) Temporal relationship between a STOC and a Ca²⁺ spark. Images (a) display the spatio-temporal evolution of the Ca²⁺ spark (Video 5). Changes in [Ca²⁺] in the images are expressed as ΔF/F₀ (percentage) and displayed on a pseudocolor scale calibrated at the right. The traces shown are the time course of signal mass (b), its time derivative calibrated to give the underlying Ca²⁺ current flowing from the intracellular Ca²⁺ store into the cytosol, i.e., I_Ca(spark) (c), and the corresponding STOC (d). The numbers above the images correspond to the time when images were acquired as indicated in the time course of signal mass. Note that the endogenous Ca²⁺ buffer as estimated in Bao et al. (2008) was taken into account in this and in Fig. 2’s calculation of signal mass and I_Ca(spark). (B) Quantitative relationships between Ca²⁺ sparks and STOCs. Scatter plots show the correlations between (a) the rise time of Ca²⁺ spark signal mass (SM) and the time between the onset of the STOC and the onset of its decay, designated as time to the onset of decay (TTOD; r = 0.8869, P < 0.0001); (b) signal mass and STOC amplitude (r = 0.404, P = 0.005), (c) I_Ca(spark) and STOC amplitude (r = 0.4451, P = 0.002), and (d) signal mass rise time and STOC amplitude (r = 0.4816, P = 0.001). n = 35 in all panels.