The effect of lidocaine on the voltage-dependent fluorescence of labeled sodium channel domains. (A) Time-dependent fluorescence changes from TMR-labeled S216C, S660C, L1115C, and S1436C channels before (left) and after (right) a 10-mM lidocaine application. Inset shows the pulse protocol. Each trace was obtained by averaging 10 trials with an interval of 1 s between pulses. The y axis in the scale bar represents percent fluorescence change (ΔF/F). L1115C fluorescence traces were inverted for comparison. (B) Steady-state F-V relationship of TMR-labeled S216C, S660C, L1115C, and S1436C channels before (black) and after (red) a 10-mM lidocaine application. Circles represent the means ± SE of at least five independent experiments, whereas the lines represent the best fits of the averaged data to a single Boltzmann function.