Fig. 2
Slow voltage-ramp-induced currents mediated by TTX-R Na+ channels in dural afferent neurons. A. Typical traces of slow voltage-ramp-induced TTX-R INa recorded in small- (a) and medium-sized (b) DiI-positive neurons. TTX-R INa were elicited by five successive voltage-ramp stimuli every 15 s (6 s duration; up to + 10 mV depolarization at a VH of -80 mV; 15 mV/s). Notably, voltage-ramp stimuli elicited “W-shaped” membrane currents, which are potentially mediated by NaV1.9 (left, arrowheads) and NaV1.8 (right, arrows). Moreover, the NaV1.9-mediated ramp currents rapidly and completely disappeared within 3 min. B. Occurrence of NaV1.8- and NaV1.9-mediated ramp currents in small- and medium-sized DiI-positive neurons. The values in parenthesis represent the number of DiI-positive neurons showing NaV1.8- and NaV1.9-mediated TTX-R IRamp. The occurrence of NaV1.8- and NaV1.9-mediated ramp currents was determined immediately after the whole-cell configuration was made. C. Concentration–response relationships of A803467 for TTX-R IRamp. The points and error bars represent the mean and SEM from eight small- and seven medium-sized DiI-positive neurons. D. a, Scatter plot of the density of TTX-R IRamp against membrane capacitance (Cm) obtained from the same neurons (n = 152). The linear trend line represents the best fit using a least-squares fit (r = 0.47). b, The mean values of the density of TTX-R IRamp in small- (S) and medium-sized (M) DiI-positive neurons. The columns and error bars represent the mean and SEM from 60 small- and 92 medium-sized DiI-positive neurons. **; p < 0.01 (unpaired t-test). E. Scatter plot of the density of TTX-R IRamp against TTX-R INaP obtained from the same neurons (n = 152). The linear trend line represents the best fit using a least-squares fit (r = 0.78). F. a, Typical traces of slow voltage-ramp-induced TTX-R INa recorded in the absence and presence of 3 μM riluzole in small- (upper) and medium-sized (lower) DiI-positive neurons. b, Concentration–response relationships of riluzole for the TTX-R IRamp. The points and error bars represent the mean and SEM from six small- and eight medium-sized DiI-positive neurons. G. a, Typical traces of slow voltage-ramp-induced TTX-R INa recorded in the absence and presence of 100 nM A803467 and 100 nM A803467 plus 10 μM riluzole in medium-sized DiI-positive neurons. b, Changes in the current density of slow voltage-ramp-induced TTX-R INa by 100 nM A803467 and 100 nM A803467 plus 10 μM riluzole. The columns and error bars represent the mean and SEM from eight medium-sized DiI-positive neurons. **; p < 0.01 (paired t-test)