Whole-cell patch-clamp recordings
Na+ currents were recorded using low-resistance, fire-polished electrodes (≈ 1MΩ) made from 8161 Corning borosilicate glass coated with HIPEC (Dow-Corning, Midland, MI, USA) to minimize electrode capacitance. An Axopatch 200 amplifier and pClamp software (Molecular Devices, Sunnyvale, CA, USA) were used to record Na+ currents. The series resistance was compensated to 80% to minimize voltage-clamp errors. The cells were allowed to stabilize for 5 min after the whole-cell configuration was established. The membrane potential was held at –140mV before the currents were recorded. Sodium Currents were filtered at 5 kHz and digitized at 83.33 kHz. The liquid junction potential was not corrected. All the experiments were performed at room temperature (22°C).