Figure 4.

Ionic and gating currents for a weakly conducting mutant Shaker Kv channel. (A) Family of ionic current records. Holding voltage was −100 mV, tail voltage was −100 mV, and depolarizations were from −100 to 50 mV, in 10-mV increments. A P/−4 protocol was used to subtract leak and linear capacitive currents. (B) Family of gating currents recorded in the presence of 1 μM Agitoxin-2. Membrane voltage was depolarized for 30 ms to various test voltages (−100 to 10 mV) and then repolarized to the holding voltage (−100 mV). A P/−4 protocol was used to subtract leak and linear capacitive currents. (C) G-V relations for Wt and F481W. Conductance was calculated from the amplitude of steady-state current before repolarization, normalized and plotted versus voltage. Smooth curves are single Boltzmann fits to the data with parameters as follows: Wt: V₅₀ = −32.8 mV, z = 3.7; F481W: V₅₀ = −41.3 mV, z = 4.4. (D) Normalized Q-V relations for W434F and F481W. Q was obtained by integrating both the ON and OFF components of gating current, taking their average and normalizing to Q_max measured at depolarized voltages. Smooth curves are single Boltzmann fits to the data with parameters as follows: W434F: V₅₀ = −47.2 mV, z = 4.1; F481W: V₅₀ = −50.2 mV, z = 3.6.