Figure 7.

Biophysical properties of the P475G mutation. (A) Representative I_ac and I_deac recordings for the mutant P475G are displayed on the left and right, respectively. (B) Representative I_Qac recording of P475G using the activation pulse protocol shown on top. (C) Voltage-dependence of BC gate opening (GV curve) and VSD movement (QV curve) for P475G. The GV curve of P475G (blue circles, n = 5) was shifted by ∼ +45 mV toward more positive potentials compared to Shaker-IR control (black dotted line). The blue line represents the average fit with a single Boltzmann equation. The QV curve of P475G (red circles, n = 4) was obtained by integrating and normalizing the I_Qac recordings obtained with activation protocol shown in panel B. Note, P475G displayed, similar to P475A, a QV curve with two gating charge components whereby the first component carried ∼78% of the gating charge and superposed on the QV curve of Shaker-IR-W434F control (black). The second component carried the remaining 22% of the gating charge and matched the GV curve (blue line). (D) Voltage-dependent time constants of BC gate opening and closure in P475G (blue) obtained by fitting I_ac with a double and I_deac with a single exponential function. The τ_I_ac (even the fast one) and τ_I_deac kinetics were clearly slower than those of Shaker-IR control (gray). Voltage-dependency of τ_I_Qac ± SE for P475G (red, n = 8) and Shaker-IR-W434F (black). (E) Increasing gradually the conditioning prepulse duration at +40 mV (pulse protocol is shown on top) resulted in P475G in a gradual decrease in I_Qdeac amplitude, which reflects a slowing down of τ_I_Qdeac. Approaching the gradual decrease in I_Qdeac with a single exponential (blue dotted line) yielded a time constant of 6.5 ms. (F) Ionic currents of P475G after pulsing to +80 mV (pulse protocol shown on top) in control condition (black), and in presence of 1 mM (red), 3 mM (green), and 10 mM (blue) 4-AP. (G) Current density of P475G in control condition (black), in presence of 1 mM (red), 3 mM (green), and 10 mM (blue) 4-AP (n = 4). Over the voltage range tested, no difference in the current density was observed upon 4-AP application.