Fig. S1.

Evidence for Ca²⁺-induced Ca²⁺ release in MTM1-deficient muscle fibers. (A) Change in cytosolic [Ca²⁺] (Δ[Ca²⁺]) and corresponding rate of Ca²⁺ release (d[Ca]_Tot/dt) calculated from line-averaged rhod-2 fluorescence signals collected while applying a 500 ms-long depolarizing pulse to –10 mV in a WT fiber (Left) and in a MTM1-deficient fiber (Right). The MTM1-deficient fiber yields a delayed onset phase of Ca²⁺ release during the pulse: Its amplitude and the corresponding threshold [Ca²⁺] level were determined as indicated. (B) Peak amplitude of the delayed onset phase of Ca²⁺ release as a function of the threshold [Ca²⁺] level. Each data point is from a separate MTM1-deficient muscle fiber.