Properties of resting [Ca ²⁺ ] _cyt in WT and R2509C-RYR1 primary myocytes. (A) Comparison of resting [Ca²⁺]_cyt in primary myocytes from WT (n = 205, N = 3), R2509C-Het (Het; n = 257, N = 3), and R2509C-Hom (Hom; n = 776, N = 4) mice. [Ca²⁺]_cyt was determined using fura-2. (B) Resting [Ca²⁺]_cyt in R2509C-Hom myocytes at 2 (176.6 ± 54.3 nM: n = 148, N = 3), 3 (179.5 ± 63.2 nM: n = 494, N = 4), and 4 (222.5 ± 100.3 nM: n = 134, N = 3) days after differentiation, and at 3 (140.6 ± 52.7 nM: n = 230, N = 3) and 4 (151.4 ± 73.5 nM: n = 151, N = 3) days after differentiation in the presence of Cpd1. Cpd1 was added at 2 µM at the onset of differentiation. Values are mean ± SD. Statistical significance was determined using one-way ANOVA with Tukey’s test. (C) Expression levels of RYR1 in R2509C-Hom myocytes. Western blotting showing RYR1 and loading control GAPDH. Molecular mass standards are shown on the right (kD). In the graph on the right, data were normalized based on the values at day 3. Data are means ± SD (N = 3) and analyzed by one-way ANOVA with Tukey’s test. “n” is the number of myocytes and “N” is the number of animals.