Fig. 2: Ca_V2.1 VSDs have diverse voltage-dependent activation properties.

a VCF recordings of Ca_V2.1 complexes (α_1A/α₂δ−1/β_2a) fluorescently labeled in VSD-I. Voltage steps (V_m) are shown on top; ionic currents (I_m) and fluorescence deflections (ΔF) were acquired simultaneously. b As in (a) for VSD-II. VSD-II does not show clear ΔF and appears to be voltage-insensitive (Figs. S1, S2). c, d As in (a) for VSD-III and VSD-IV, respectively. e As in (a) for control channels (no substituted Cys). f Voltage dependence of VSD-I activation (normalized ΔF, blue triangles) and fit to the sum of two Boltzmann distributions (blue curve, Eq. 3). Voltage dependence of pore opening (normalized I_tail, Eq. 1) for VSD-I-labeled channels (gray circles and curve). The voltage dependence of pore opening for control channels is shown as black dashed curve. All voltage-dependence parameters are in Table 1. g As in (f), for VSD-III (green; Eq. 2). h As in (f), for VSD-IV (orange). i Overlay of all voltage dependences observed on the human α_1A subunit. Blue: VSD-I; green: VSD-II; orange: VSD-IV; black: pore opening (from wild-type channels). VSD-II activation is shown as a flat red line. Error bars are S.E.M.