Permeabilized myocytes from PMIs show similar Ca²⁺ load but higher Ca²⁺ sparks per load unit than sham cells. (A; top) Line-scan images of representative caffeine-evoked Ca²⁺ release in permeabilized myocytes from sham (left) or from PMI (right) mice. (Bottom) Caffeine-evoked Ca²⁺ transient peak (F/F₀) of permeabilized myocytes from sham (gray bar; n = 14 cells from three animals) and PMI (dark red bar; n = 15 cells from three animals) mice. (B) Ca²⁺ spark frequency normalized to SR load in permeabilized cells from sham (gray bar; n = 13 from three animals) and PMI mice (dark red bar; n = 12 cells from three animals). (C) Ca²⁺ spark frequency normalized to SR load in intact cells from sham (white bar; n = 10 from four animals) and PMI mice (red bar; n = 9 cells from four animals). *, P < 0.05 versus myocytes from sham mice. Error bars represent the SEM.