Figure 4.

GC displacement (blue), S4 Z (red), and macroscopic current (black). Normalized simulated current (black circles) and the sum of tetramer S4 Z displacements (red circles) in 2000 iCh, 4 s past depolarization (for the protocol in the inset), are given. The black line represents experimental data (24). The S4 Z data are fitted with two sigmoidal curves at negative and positive $V_m$, representing the I and II movements of S4, respectively. At positive $V_m$, an increasing fraction of S4 in the 2000 iCh transitions to the II movement. GC displacement associated with one representative iCh S4 Z transition is calculated based on two selections: the entire IKs (${\text{Q}}_{total}$, dark blue) and S3-S4 segments only (${\text{Q}}_{S3-S4}$, light blue) at different $V_m$. The GC data are fitted with a single sigmoid (light and dark blue traces), analogous to the S4 Z data at negative $V_m$.