Effect of RyR1 inhibitors on DICR activity. (A) Chemical structures of dantrolene, Cpd1, and procaine. (B) Typical results of R-CEPIA1er fluorescence in cells without (control, left) or with 10 μM dantrolene (center) or 5 mM procaine (right). High [K⁺] solution ranging from 5 to 61 mM (symbols shown in left) was applied at 30 s after starting (blue arrowheads). (C) [K⁺] dependence of fluorescence change (F/F₀) in cells without (Cont, black) or with 10 μM dantrolene (Dan, red), 3 μM Cpd1 (Cpd1, blue), or 5 mM procaine (Pro, green). Data are means ± SD (n = 9, N = 3). (D and E) Fluorescence change by 61 mM K⁺ (D) and EC₅₀ values for [K⁺] (E). Data are means ± SD (n = 9, N = 3) and were analyzed by one-way ANOVA with Dunnett’s multiple comparisons test. (F) Caffeine dependence of R-CEPIA1er fluorescence (F/F₀) in cells without (control, black) or with 10 μM dantrolene (Dan, red), 3 μM Cpd1 (Cpd, blue) or 5 mM procaine (Pro, green). Data are means ± SD (n = 9, N = 3). (G and H) Fluorescence change by 20 mM caffeine (G) and EC₅₀ values for caffeine (H). Data are means ± SD (n = 9, N = 3) and were analyzed by one-way ANOVA with Dunnett’s multiple comparisons test. n is the number of wells and N is the number of independent experiments.