Effects of the LA lidocaine on NaChBac currents. (A) A current-voltage relationship curve for wild-type NaChBac is shown for Xenopus oocytes expressing NaChBac channels held at a holding potential of −120 mV. Currents were activated by 100 ms of depolarizing pulses from −100 to 100 mV in 10-mV increments followed by repolarization to −120 mV. n = 4. Representative current traces are shown in the inset. Bar: horizontal, 20 ms; vertical, 2 µA. (B) A concentration response curve was generated with the mean of I_drug/I_control obtained from the peak currents after exposing cells to 30 µM, 100 µM, 300 µM, 1 mM, and 3 mM lidocaine. The IC₅₀ for lidocaine according to the concentration response curve is ∼260 µM. Representative current traces obtained after depolarization from the holding potential −120 to −20 mV in the presence of various lidocaine concentrations (0 µM, 100 µM, 300 µM, and 1 mM) on oocytes expressing wild-type NaChBac channels are shown in the bottom inset. Currents are normalized to the peak amplitude of the control trace. The dashed line indicates the zero current level. The top inset is a chemical structure of lidocaine. n = 4. Bar, 500 ms. (C) Diary plot showing normalized peak current inhibition resulting from extracellular application of 1 mM lidocaine while holding the cells at −120 mV for 3 min. In the presence of 1 mM lidocaine, a 1,500-ms depolarizing pulse to −20 mV was performed. Depolarizing pulses were followed by a 5-min Ringer’s solution wash while holding the cells at −120 mV. Representative current traces are shown with the zero current lines (dotted lines). Bar, 500 ms. (D) Conductance-voltage relationship curves are shown for control (●) and after 1 mM lidocaine exposure (○). A significant left shift (P < 0.05) is observed in the SSI curve after 1 mM lidocaine exposure (□) as compared with the control (■). n = 5. Error bars represent SEM.