Kv1.2–Kv1.5 chimera channels lack the slow fluorescence quenching at negative potentials. (A) Cartoon representation of Kv1.2 A291C (top), Kv1.5 WT (bottom), and the two chimeric channels (middle cartoons). Open squares (and their connecting segments) originate from Kv1.2, and slashed squares are Kv1.5 segments. A291C is located approximately with closed circles at the N-terminal S4. (B) Representative fluorescence traces from the Kv1.5-S12L-Kv1.2 A291C chimera. Data were collected using the protocol outlined in Fig. 2. (C) Overlay of representative fluorescence deflections for Kv1.2 A291C and Kv1.5-S12L-Kv1.2 (S12L) A291C for depolarizations to 30 mV normalized to the fast fluorescence quenching components. The inset shows overlays of deactivating ionic tail currents and off-fluorescence of Kv1.5-S1S2L-Kv1.2 A291C (top) and Kv1.2 A291C (bottom), with scale bars as noted. (D) Mean normalized G-V (closed symbols) and F-V (open symbols) relationships for the Kv1.5/Kv1.2 chimera channels compared with Kv1.2 A291C, shown ±SEM (n = 10–13). Boltzmann fits to the data from Kv1.5-S12L-Kv1.2 A291C (S12L) gave V_1/2 and k values of 2.6 ± 2.6 mV and 23.9 ± 0.9 mV and −40.3 ± 3.1 mV and 28.4 ± 2.6 mV for G-V and F-V, respectively; the fits to Kv1.5-S23L-Kv1.2 A291C (S23L) were 7.3 ± 1.9 mV and 23.9 ± 0.7 mV for the G-V relationships and −40.9 ± 2.2 mV and 23.4 ± 2.3 mV for the F-V relationships. Kv1.2 A291C values are as reported in Fig. 4. (E) Voltage-dependence plots of the fast fluorescence component of Kv1.5-S23L-Kv1.2 A291C with that of Kv1.2 A291C from Fig. 5 C. V_1/2 and k values were −40.3 ± 2.2 mV and 19.5 ± 1.7 mV for the chimera channel (n = 15–17). (F) Mean normalized F-V relationship of the fast component of Kv1.5-S23L-Kv1.2 A291C emission, overlaid with the Kv1.2 Q-V relationship (closed circles) from Fig. 6 B.