Fig. 2: Characterization of time and voltage-dependent properties of the four CaV1.1 voltage-sensing domains.
From: The molecular transition that confers voltage dependence to muscle contraction
a Representative Ca2+ currents (ICa) and simultaneously recorded fluorescence signals from human CaV1.1 channels complex (α1S + β1a + α2δ-1 + γ1 + Stac3) reporting local protein structural changes in each VSD. Above the recordings are the step voltage protocol used and the labeling position in the pore-forming α1S subunit of CaV1.1 channels structure (Protein Data Bank ID 5GJV;53, top view). The black lines superimposed to the fluorescence traces at 20 mV are best fits to a single (VSD-I, -III, and -IV) or double exponential functions (VSD-II). b Mean normalized fluorescence representing the VSD activation probabilities during a skeletal muscle AP waveform. For comparison, all the fluorescence traces are presented as positive deflections. An animation combining these AP-clamp data on the CaV1.1 structure is shown in Supplementary Movie 1. c The time constant (τ) of VSD activation to 20 mV. For VSD-II, the relative amplitudes (Amp%) of fast and slow components are reported above the τ values (VSD-I: n = 9, VSD-II: n = 5, VSD-III: n = 9, VSD-IV: n = 6). d VSDs activities at resting membrane potential (Vm). Note the elevated activity of VSD-IV at resting membrane potential (VSD-I: n = 6, VSD-II: n = 4, VSD-III: n = 5, VSD-IV: n = 6). e Maximal VSD activity recorded during AP-clamp from experiments as in (b). Note that only fast-activating VSD-III and -IV respond to an AP stimulus. (VSD-I: n = 6, VSD-II: n = 4, VSD-III: n = 5, VSD-IV: n = 6). Error bars are ± SEM.
