Fig. 6. Simple models of AIS-specific spiking properties.
(A) A cylindrical single-compartment model was equipped with either Nav1.1 or Nav1.6 channels. (B) Firing rate in response to a current injection of 10 pA was higher when Nav1.6 channels were inserted into the model. Gray arrows indicate spontaneous spiking. Scale bar, 50 ms/20 mV. (C) Phase plots derived from (B) reveal a lower threshold for the Nav1.6 model than for the Nav1.1 model. Scale bar, 20 mV/200 V/s. (D) Left: A 1-mm axon model was created with 201 compartments. All compartments were uniform except each had only Nav1.6 channels or only Nav1.1 channels; the percentage of compartments with Nav1.6 channels increased from 0 (top) to 100% (bottom) across different simulation trials; Nav1.6 channels were always centered around the middle compartment. Right: Spiking response to a 10-pA current injection into the center compartment for the four configurations on the left. Scale bar, 200 ms/20 mV. (E) Firing rate (top), threshold depolarization (middle), and spontaneous firing rate (bottom) at the center compartment as a function of the Nav1.6 portion within the axon.