Excitability is increased in DRG neurons transfected with the P1308L or V1298F mutant channels. A, Responses of DRG neurons expressing WT, P1308L, or V1298F channels to a series of current stimuli with 5-pA increment. DRG neurons expressing P1308L channels showed a lower action potential threshold (P1308L: 122 ± 10 pA, n = 50, p < 0.001 vs WT: 188 ± 14 pA, n = 38), while expression of V1298F did not significantly change the action potential threshold (V1298F: 154 ± 18 pA, n = 27, p = 0.215 vs WT). B, The mean firing frequency of DRG neurons expressing WT, P1308L, or V1298F channels in response to a series of 1-s current injections ranging from 25 to 500 pA with 25-pA increments. Both P1308L and V1298F elevated firing frequency of transfected DRG neurons. * indicates p < 0.05 for P1308L vs WT channels, * indicates p < 0.05 for V1298F vs WT channels. C, Representative traces showing responses to current stimuli approximately 1.5× (top) and 2× (bottom) action potential threshold, recorded from DRG neurons expressing WT, P1308L, or V1298F channels from (A).