(a) Representative example of the time course of the reduction in fluorescence intensity upon N-AT application. The fluorescence intensities shown is the fluorescence measured at +80 mV (during repeated applications of the voltage protocol used to measure the complete F(V) as in panel c), normalized to the fluorescence intensity at +80 mV recorded in the first F(V) in control solution. Red symbols denote control (without N-AT) and purple symbols denote in the presence of N-AT. The fluorescence signal reduces with time in the presence of N-AT. In contrast, the fluorescence signal is preserved in the absence of N-AT (red symbol, recorded in another cell). (b) Summary of fluorescence emission monitored from unbound Alexa488 in control solution and in taurine-supplemented control solution (0.25 or 0.5 M taurine). In these experiments, no oocytes or channels were present. A.U. denotes arbitrary units. Data as mean ± SEM. n = 3. (c) Mean F(V) curve for KV7.1/G219C*/S225L+KCNE1 in the absence (red symbols, data from Figure 3B) or presence of 70 µM N-AT. The holding voltage is –80 mV, the pre-pulse –160 mV for 5 s, and test voltages between –160 and +100 mV for 5 s in 20 mV increments. The tail voltage is –40 mV. Each F(V) curve is normalized between 0 and 1 based on the bottom and top deduced from the double Boltzmann fits for each curve (see Materials and methods). Data as mean ± SEM. n = 3 for N-AT.