FIGURE 4.

Ryanodine does not promote Ca²⁺ leakage from the SR in cultured neonatal cardiomyocytes. A, actual traces depicting the change in Fura-2 AM fluorescence ratio (340/380 nm) in cells treated with thapsigargin (TG, 1 μm in Ca²⁺-free saline) in the absence (n = 32 cells, top left panel) and presence of ryanodine (Ry, 10 μm, 30-min incubation, n = 29 cells, top right panel). Caffeine (Caff, 10 mm) did not modify basal Ca²⁺ levels in ryanodine-pretreated cells (n = 26 cells, bottom left panel). A comparison between the averaged traces obtained in the two treatment situations is depicted in the bottom right panel of A (p > 0.05, Mann Whitney U test). B, comparison of the increases in fluorescence ratio (340/380 nm) of Fura-2 AM-incubated neonatal cardiomyocytes in the treatment conditions mentioned in A. C, comparison between the times necessary to reach the maximal effect (τ) and the times in which the fluorescence ratio decreases to the half maximal level (τ/2) in the above-mentioned treatment cases. p > 0.05, one-way analysis of variance followed by Bonferroni and Tukey tests. D, comparison of the averaged areas under the curve of the traces presented in the top panels of A. p > 0.05.