Voltage-sensitive sodium channels: agents that perturb inactivation gating.

In summary, the voltage-sensitive sodium channel from eel electroplax provides an optimal preparation for biochemical and biophysical studies of molecular structure and gating. We have demonstrated that the purified and reconstituted protein is capable of functioning normally, exhibiting, among other properties, voltage-dependent activation and inactivation gating mechanisms. We have been able to recreate the classical electrophysiological studies in which inactivation gating can be removed by proteolytic modification of the cytoplasmic surface of the molecule, and have mapped the probable site of modification to the peptide segment lying between subunit domains III and IV. We have demonstrated that the reconstituted protein undergoes interactions with the lidocaine derivative QX-314 which, at low concentrations, results in paradoxical activation of the channel and a facilitation of modification by oxidizing reagents that remove inactivation gating.