(A) Line scans of Fluo-4 fluorescence from permeablized EDL muscle fibers (young: upper panel; aged: middle panel; aged +S107: lower panel) showing Ca2+ spark activity. The heat diagram indicates the normalized change in fluorescence intensity (ΔF/F0). (B) Bar graph showing average Ca2+ spark frequency (the number of sparks examined were: 1219 in the young mice, n = 530 line scans from 32 fibers and 6 animals; 7389 in the vehicle-treated aged mice, n = 505 line scans from 30 fibers and 6 animals; 3713 in aged mice treated with S107, n = 414 line scans from 25 fibers and 5 animals; 673 in the untreated RyR1-S2844D mice, n = 240 line scans from 15 fibers and 3 animals; 2405 in S107 treated RyR1-S2844D mice, n = 210 line scans from 14 cells and 3 animals; mean, ± SEM, *** P < 0.001 (ANOVA).