Spontaneous Excitation Patterns Computed for Axons with Injury-like Impairments of Sodium Channels and Na/K Pumps
Figure 4
Transitions between STO and burst behaviors.
(A) Upper: Vm (black solid line) at an injured node and the varying EIon (ENa and EK; blue dotted lines). Three gNa populations are used: LSi = [0,2,26.5]mV and fi = [0.72,0.08,0.2] with Voli = Volo = 10−15 m3. Initiation and termination times of a burst of spikes (pink star, green dot, respectively) are used in Figure 5. Lower: corresponding Na+ currents, as labelled. (B) Equilibrium values of Nav channel activation and inactivation variables, mi and hi. (C) The steady-state open probabilities, : with a mild injury gwindow(V) magnitude is slightly less at 0 mV (vertical line and circles) but much enlarged at voltages near the normal RP (−65.5 mV for fixed [ion] condition). (D) Another example: LSi = [0,2,20]mV and fi = [0.72,0.08,0.2] and Voli = Volo = 3×10−15 m3, with expanded detail showing STOs. Note the difference of time scales in (A) and (D), reflecting the fact that a 3-fold lower axonal surface-to-volume ratio in (D) slows the rate of [ion] changes.