NaN/Nav1.9 current is flowing during the long-lasting depolarization plateau. (A, top) Voltage command taken from current clamp experiment in a small DRG neuron (28 pF) expressing both SNS/Nav1.8 and NaN/Nav1.9 in response to a short depolarizing stimulus (+85 pA, 5 ms, not depicted) and further used as a voltage command clamping the neuron. (bottom) Total inward current elicited during the long-lasting depolarization plateau and discharge waveform (right) or stepped protocol (left) in the same cell. The inset shows the steady TTX-R Na⁺ current (putative NaN/Nav1.9) flowing during the plateau phase. [Na⁺]_o = 60 mM. (B, top) The voltage command waveform as in A was injected into a small DRG neuron (32 pF) that expresses SNS/Nav1.8 but not NaN/Nav1.9. (bottom) SNS/Nav1.8 current elicited during the long-lasting depolarization plateau and discharge waveform (right) or the stepped protocol (left). [Na⁺]_o = 60 mM. The inset shows the weak activation of SNS/Nav1.8 during the plateau phase. (C) Dynamic clamp test of partial currents in a simulated small DRG neuron containing NaN/Nav1.9, SNS/Nav1.8, M/KCNQ, KDr, and leak conductances (see Materials and methods for further details) commanded by a long-lasting depolarization plateau waveform. (bottom) Simultaneous SNS/Nav1.8 and NaN/Nav1.9 currents generated in the simulated DRG neuron during dynamic clamp with the voltage command waveform. E_Na = +60 mV. Recordings in A and B made using the intracellular solution 1 (Table I; 100 mM CsCl, 30 mM CsF, 0 mM KCl).