Biophysical characterisation of the persistent sodium current of the Nav1.6 neuronal sodium channel: a single-channel analysis

Na(v)1.6 is the major voltage-gated sodium channel at nodes of Ranvier. This channel has been shown to produce a robust persistent inward current in whole-cell experiments. Na(v)1.6 plays an important role in axonal conduction and may significantly contribute to the pathophysiology of the injured nervous system through this persistent current. However, the underlying molecular mechanisms and regulation of the persistent current are not well understood. Using the whole-cell configuration of the patch-clamp technique, we investigated the Na(v)1.6 transient and persistent currents in HEK-293. Previous studies have shown that the persistent current depended on the content of the patch electrode. Therefore, we characterised the single-channel properties of the persistent current with an intact intracellular medium using the cell-attached configuration of the patch-clamp technique. In HEK-293 cells, the Na(v)1.6 persistent current recorded in the whole-cell configuration was 3-5% of the peak transient current. In single-channel recording, the ratio between peak and persistent open probability confirmed the magnitude of the persistent current observed in the whole-cell configuration. The cell-attached configuration revealed that the molecular mechanism of the whole-cell persistent current is a consequence of single Na(v)1.6 channels reopening.