Effect of AM-2099 on action potentials in human DRG neurons.

A, Action potentials evoked by a short (0.5-ms) current injection before and after application of 600 nM AM-2099. Stimulating current was adjusted to be slightly larger in AM-2099 so that the voltage immediately after cessation of the stimulating current was the same as in control (because control has an active component in the last 0.1 ms of the stimulating pulse that is inhibited with AM-2099). B, Phase-plane plot of dV/dt versus V showing reduction of maximum upstroke velocity and peak. Upper dashed lines: maximum upstroke velocity in control (black) and with 600 nM AM-2099 (red). C, Collected results for effect of 600 nM AM-2099 on the maximal upstroke velocity of the action potential in 18 neurons. D, Collected results for effect of 600 nM AM-2099 on peak of the action potential evoked by a short current injection. E, Collected results for effect of 600 nM AM-2099 on the width of the action potential measured at 0 mV. In cells with values only in control, the action potential in AM-2099 had a peak < 0 mV.

Effect of AM-2099 on action potential threshold.

Short (0.5-ms) current injections of different size were delivered, with gradations to find the level of current injection that first evoked an action potential. The voltage immediately after the smallest current injection that evoked a spike was considered as the threshold voltage. A, Just sub-threshold and supra-threshold current injections in control (left) and after application of 600 nM AM-2099 (right). B, Collected data for threshold voltage before and after 600 AM-2099 (n=18). C, Collected data for minimum current (0.5-ms current injection) that evoked an action potential (n=18).

Effect of 600 nM AM-2099 on rheobase and repetitive firing.

A, Firing evoked by 1-s injections of current of increasing magnitude in control and after application of 600 nM AM-2099. B, Number of action potentials as a function of the injected current before and after 600 nM AM-2099 in this neuron. Asterisks indicate rheobase current in control (black) and in AM-2099 (red). C, Collected data for the effect of 600 nM AM-2099 on rheobase current. D, Collected results for the effect of 600 nM AM-2099 on the maximal number of action potentials during 1-s current injections over a range of magnitudes for neurons that fired more than one action potential in control. Dashed line drawn at 1 action potential.

Prolongation of refractory period by AM-2099.

A, Action potentials were evoked by a pair of 0.5-ms current injections with a variable time between them, with magnitude of both set at 1.5-times the threshold current determined in control. The time between the two current injections was varied from longer to shorter to determine the refractory period with this stimulus. The figure shows superimposed sweeps from 11 different sets of times in control (black) and with 600 nm AM-2099 (red). In control, the second stimulus evoked an action potential with a spacing (start to start) of 20.6 ms, while after AM-2099, a spacing of 35.2 ms was required to evoke an action potential using the same stimuli. B, Collected results in 15 neurons.

Comparison of Nav1.7 and Nav1.8 inhibition on action potential firing in human DRG neurons.

A, Change in action potential threshold by inhibiting Nav1.7 channels (600 nM AM-2099) or Nav1.8 channels (10 nM VX-548). B, Inhibition of maximum upstroke of action potential by inhibiting Nav1.7 channels (600 nM AM-2099) or Nav1.8 channels (10 nM VX-548). C, Reduction of action potential peak by inhibiting Nav1.7 channels (600 nM AM-2099) or Nav1.8 channels (10 nM VX-548). D, Effect of inhibiting Nav1.7 channels (600 nM AM-2099) or Nav1.8 channels (100 nM VX-548) on maximum number of action potentials evoked by 1-s depolarizations of different magnitudes. Data for effects of 100 nM VX-548 from Stewart et al., 2025.