Activation. Peak current elicited by the P1 pulse from a two-pulse protocol (see Fig. 1, inset) plotted versus V to generate I-V relationships for (A) Kv1.4 (■, n = 9), Kv1.4[P558G] (●, n = 23) and Kv1.4[P558A] (▴, n = 6); and (B) Kv1.4ΔN (□, n = 6), Kv1.4[P558G]ΔN (○, n = 16), and Kv1.4[P558A]ΔN (Δ, n = 17) (error bars smaller than symbols). (C) Replotted for easy comparison are Kv1.4[P558G] (●), Kv1.4[P558G]ΔN (○), Kv1.4[P558A] (▴), and Kv1.4[P558A]ΔN (Δ) activation. Activation of Kv1.4[P558A] was well fit by a single exponential and Kv1.4[P558A]ΔN was well fit by a double exponential. (D) Time constants for Kv1.4[P558A] with 2 (■, n = 7) and 98 mM (○, n = 7) [K+]o. (E) Kv1.4[P558A]ΔN fast and slow time constants in 2 mM [K+]o (fast: ●, slow: ■, n = 7) and 98 mM [K+]o (fast: ○, slow: □, n = 7). (F and G) Fast (F) and slow (G) time constants of activation of Kv1.4[P558G]ΔN.