Figure 4. The underlying effect of 4-AP on non-burst neurons.

At a holding potential of −80 mV, a depolarizing step current injection in the presence of TTX produced either no depolarizing potential (n= 6) or a transient depolarizing potential (n= 5) in non-burst neurons (n= 11). A, in TRN neurons that produced no transient depolarization in TTX, 4-AP (5 mm) produced no unmasking of a transient response in 3 of 6 neurons, but unmasked a small depolarization in the remaining 3 neurons (weak unmasking). B, in non-burst neurons that produced small depolarizing potentials in TTX, 4-AP (5 mm) application increased the small depolarization in all 5 neurons in a reversible manner. In 2 of 5 cells, 4-AP application unmasked a normal appearing low threshold Ca²⁺ spike. Dashed line indicates −80 mV. The bottom traces (I) indicate depolarizing current steps.