Properties of TTX-R Na⁺ currents in Nav1.9^−/− DRG neurons. Families of current traces elicited in a 33 pF Nav1.9^+/+ DRG neuron (A) and a 29 pF Nav1.9^−/− DRG neuron (B). Currents were evoked by 100-ms depolarizing voltage steps from −80 to −55 mV in 5-mV increments from a holding potential of −100 mV. (C) Scatterplot showing the amplitude of the TTX-R Na⁺ current recorded at −60 mV in small Nav1.9^+/+ and Nav1.9^−/− DRG neurons. The bars indicated the mean amplitude ± SEM. ***, P < 0.001. (Inset) examples of currents evoked at −60 mV in two representative Nav1.9^+/+ and Nav1.9^−/− neurons. (D) Whole-cell currents elicited in the Nav1.9^+/+ neuron shown in A by a 8-s ramp depolarization from −120 to 0 mV (rate, 15 mV s⁻¹), after 30-s conditioning at −100 mV (red trace) or −50 mV (black trace). (E) SNS currents elicited by a 1.6-s ramp depolarization from −120 to 0 mV (rate, 75 mV s⁻¹) in the Nav1.9^−/− neuron shown in B. (F) Comparison of ramp-activated SNS currents in Nav1.9^+/+ (red trace) and Nav1.9^−/− (black trace) DRG neurons. Each trace is the average of four different cells, and currents were normalized to facilitate comparison. Ramps were applied from −120 to 0 mV at a rate of 75 mV s⁻¹. In Nav1.9^+/+ neurons, SNS currents were isolated from NaN currents as in D. Recordings made using the intracellular solution 1 (Table I; 100 mM CsCl, 30 mM CsF, 0 mM KCl).