Figure 7.

Terfenadine-sensitive persistent firing in the absence of voltage-gated Na⁺ channels. A, Ca²⁺ spikes evoked by depolarizing steps following application of 1 μm TTX, 100 μm 4-AP, and 2 μm CCh. B, Terfenadine blocks persistent Ca²⁺ spiking activity triggered by a depolarizing step. C, Plot of the probability of triggering persistent Ca²⁺ spikes before and after Terf treatment. ***p = 1.41E-06, T = 15, df = 7, paired t test. D, Plot of input resistance assayed using a single hyperpolarizing step in TTX + 4-AP, following CCh treatment (blue) and following the subsequent addition of Terf (orange). Example step responses shown above plot. *TTX/CCh: p = 0.0463, T = 2.89, df = 7; *CCh/CCh+Terf: p = 0.0458, T = 2.90, df = 7; paired t test. E, Plot of the number of Ca²⁺ spikes evoked by the conditioning step before and after Terf (p = 0.36; paired t test). F, The underlying ADP response in TTX + 4-AP + CCh is associated with an increase in input resistance assayed using trains of positive current pulses. Terfenadine attenuates both the ADP and the related increase in input resistance. Example R_In estimates indicated in F are detrended. G, Summary plot of the change in input resistance from 4 experiments similar to F using positive current test pulses. H, Summary of change in input resistance following conditioning depolarizing step using both trains of positive and negative current pulses. *Positive pulses: p = 0.023, T = 4.31, df = 3; **negative pulses: p = 0.015, T = 5.12, df = 3; paired t test.