Maximum rate of Mn ²⁺ quench in FDB fibers in the presence or absence of pharmacological SR Ca ²⁺ store depletion. (A) Representative traces of fura-2 fluorescence during application of 0.5 mM Mn²⁺ recorded in FDB fibers isolated from WT (n = 13 fibers), CASQ1-null (n = 14 fibers), and dCASQ-null (n = 11 fibers) mice following store depletion with 1 μM thapsigargin and 15 μM cyclopiazonic acid (+depletion, i.e., maximum SOCE). (B) Quantitative analyses of the maximum rate of Mn²⁺ quench in store-depleted fibers. (C) Frequency histogram of percentage of FDB fibers exhibiting different levels of maximal rate of Mn²⁺ quench. (D) Representative traces of fura-2 fluorescence during application of 0.5 mM Mn²⁺ recorded in FDB fibers isolated from WT (n = 7 fibers), CASQ1-null (n = 14 fibers), and dCASQ-null (n = 14 fibers) mice in the absence of store depletion (–depletion, i.e., constitutive SOCE). (E) Quantitative analyses of the maximum rate of Mn²⁺ quench in the absence of store depletion. (F) Frequency histogram of percentage of FDB fibers exhibiting different levels of maximal rate of Mn²⁺ quench. Data are shown as mean ± SEM. Statistical significance: B: *, P = 0.0052, WT vs. CASQ1-null; *, P = 0.0005, WT vs. dCASQ-null; F: *, P = 0.00024, WT vs. CASQ1-null; *, P = 0.0000064, WT vs. dCASQ-null. Number of mice used: WT (n = 4); CASQ1-null (n = 5); dCASQ-null (n = 4).