Figure 4.

Effects of MinK deletion mutants on KvLQT1. (A) Voltage-clamp recordings of Xenopus oocytes expressing (from left to right) KvLQT1+MinK, KvLQT1+MinK CΔ94–129, KvLQT1+MinK CΔ79–129, or KvLQT1 alone. Activation protocol was the same as in Fig. 1. Icons represent MinK with the last amino acid indicated. (B) Normalized isochronal (t = 2 s) activation curve for KvLQT1, KvLQT1+MinK, KvLQT1+MinKCΔ94–129, and KvLQT+MinK CΔ79–129. Experimental data points were fit with the function 1/[1 + exp(V − V_1/2)/k], which gave the following apparent V_1/2 and slope factors: KvLQT1+MinK: V_1/2app = 29.4 ± 1.6 mV, k = 16.4 ± 1.6; KvLQT1+MinK CΔ94–129: V_1/2app = 29.3 ± 1.2 mV, k = 14.0 ± 1.1; KvLQT1+MinK CΔ79–129: V_1/2app = 18.4 ± 1.5 mV, k = 19.5 ± 1.4 (n = 5). Error bars represent SEM. (C) Representative tail current tracings from oocytes expressing KvLQT1 (top, left), KvLQT1+MinK (top right), KvLQT1+MinK CΔ94–129 (bottom left), and KvLQT1+MinK CΔ79–129 (bottom right). Tail currents were elicited by a 4-s +40-mV prepulse, followed by repolarization to −70 mV. (D) Voltage dependence of deactivation time constants for KvLQT1, KvLQT1+MinK, KvLQT1+MinK CΔ94–129, and KvLQT1+MinK CΔ79–129. Time constants were determined from a monoexponential fit of tail currents elicited via the deactivation protocol used in Fig. 1. For KvLQT1+MinK and KvLQT1+MinK deletion mutants, tail currents were fit over a 2-s interval immediately after repolarization. For KvLQT1, tail currents were fit starting at the peak of the tail current hook (n = 5). Error bars represent SEM.