Effects of Ts3 in the fluorescence changes that track the movement of the S4 segment of domain IV of mutant channels S1436C stained with TMRM. Holding potential was −80 mV and the test pulse was preceded by a 200-ms pulse to −90 mV. (A) Representative sodium currents recorded at −20 mV before and after the treatment with 2 μM Ts3. (B) Representative fluorescence signals obtained at −20 mV before and after the treatment with 2 μM of Ts3. The signals are shown as ΔF/F (%), where F is the fluorescence background. The arrow indicates the direction in which fluorescence increases. These experiments were performed at room temperature.