Fig. 3: VSD-I and -III display the same voltage dependence of RyR1-mediated Ca²⁺ release.

a Mean voltage dependence of VSD activation from experiments as in Fig. 2a. Lines represent fits to single Boltzmann distributions (data are represented as mean ± SEM, error bars when not visible are within the symbols; fitting parameters are reported in Supplementary Table 2). Note that each VSD exhibited distinct voltage-dependent properties (VSD-I: n = 9, VSD-II: n = 5, VSD-III: n = 10, VSD-IV: n = 6, G(V): n = 6). b Voltage dependence curves from panel (a) superimposed together with the voltage dependence of the Ca²⁺ release flux curves (black lines) from mammalian adult skeletal muscle fibers for comparison. The reported curves (black lines) were constructed from the Boltzmann distribution fit parameters in (i) Ferreira-Gregorio et al., 2017: V_1/2 = − 30 mV, z = 2.85 e₀¹⁸, (ii) Szentesi et al., 1997: V_1/2 = − 29.5 mV, z = 2.7 e₀¹⁶, (iii) Hernandez-Ochoa et al., 2014: V_1/2 = − 24 mV, z = 1.92 e₀¹⁷, (iv) Struk et al., 1998: V_1/2 = − 14 mV, z = 3.25 e₀¹⁵, (v) DiFranco et al., 2022: V_1/2 = − 13 mV, z = 3.13 e₀¹⁹. The yellow highlighted area delimits the ranges of membrane potentials where the Ca²⁺ release flux occurs. Note that only VSD-I and -III activate with a voltage dependence similar to that of SR Ca²⁺ release.