Persistent sodium current

Biophysics

Persistent sodium current generation is hypothesized to occur by the incomplete inactivation of the voltage-gated sodium channel current (INa), where the channel becomes constitutively active and conducts sodium, creating a "persistently active" inward sodium current. Upon depolarization, the four identical motifs of the sodium channel (which contain six transmembrane segments that include a pore-forming loop and a voltage sensor) move outward to allow for sodium influx. Sodium channels have the intrinsic ability to close rapidly following depolarization, and this current, named the "transient sodium current" is large and contributes to the bulk of the action potential. However, electrophysiological recordings which isolate INa find small amounts of current following depolarization which slowly inactivates, therefore contributing to the "persistent" or "non-inactivating" sodium current. The persistent sodium current also functions at sub-threshold voltages and is not only measured on depolarization of the membrane, and therefore may modulate neuronal excitability during the interspike interval of action potentials.