Reduction of electrically evoked and 4-CMC–induced RYR1-mediated Ca²⁺ release in indo-1–loaded FDB fibers from IT/+ mice. (A) Representative indo-1 ratio traces for FDB fibers from WT (top) and IT/+ (bottom) mice during successive electrical stimulation (arrowheads) and the application of 500 µM 4-CMC (black bar). (B) Average (±SEM) peak electrically evoked Ca²⁺ transients in FDB fibers from WT (n = 33; black bar) and IT/+ (n = 32; gray bar) mice. (C) Average (±SEM) peak 4-CMC–induced Ca²⁺ responses in FDB fibers from WT (n = 61; black bar) and IT/+ (n = 98; gray bar) mice. (D) Expanded time course of the rising phase of the indo-1 ratio during the application of 500 µM 4-CMC in representative FDB fibers from WT and IT/+ mice. For clarity, each trace is truncated after reaching the peak response. (E) Average (±SEM) peak of the first derivative of the rising phase of 4-CMC–induced Ca²⁺ responses in FDB fibers from WT (n = 61; black bar) and IT/+ (n = 98; gray bar) mice. *, P < 0.01.