Measurements of total releasable Ca²⁺ store content and luminal free SR Ca²⁺. (A and B) Representative superimposed fura-FF fluorescence traces (A) and quantitative analyses of total releasable Ca²⁺ store content (B) elicited during application of Ca²⁺ release cocktail (ICE). (C) Representative immunofluorescence confocal image for D1ER (green) and α-actinin (red) in an FDB fiber from a WT mouse. (D) Representative D1ER emission (Em₄₈₀ and Em₅₃₅) and D1ER_535/480 ratio traces during the 1st (upper) and 40th (lower) stimulus train recorded from a representative FDB fiber of a CASQ1-null mouse. (E and F) Quantitative analyses of the average resting D1ER ratio (D1ER_535/480; E) and time course change of D1ER_535/480 during 40 consecutive stimulus trains (F) in FDB fibers from WT and CASQ1-null mice in the presence or absence of 10 µM BTP-2. Data are shown as mean ± SEM; *, P < 0.05, WT compared with both CASQ1-null and CASQ1-null + BTP-2. #, P < 0.05, CASQ1-null compared with CASQ1-null + BTP-2. Numbers in bars (n) indicate the number of FDB fibers analyzed. Number of mice: n = 6 WT; n = 4 WT + BTP-2; n = 3 CASQ1-null; n = 3 CASQ1-null + BTP-2.