Human SCN10A Stable Cell Line - CHO

Nav1.8 (also known as SCN10A) sodium channels are expressed in nociceptive neurons, and clinical trials have shown that certain Nav1.8 inhibitors can significantly alleviate pain. Several Nav1.8 inhibitors exhibit an unusual form of state-dependence in which depolarization relieves their inhibitory effect. Here, researchers compared the state-dependent effects of various Nav1.8 channel inhibitors to determine whether inhibition is relieved-resulting in "reverse use-dependence"-during action potential (AP) firing under physiological conditions. At 37°C, the inhibitory effect of A-887826 was significantly relieved when an AP waveform was applied at a frequency of 20 Hz. In contrast, neither Suzetrigine (VX-548) nor LTGO-33 showed relief of inhibition during AP train firing, although prolonged, strong depolarization did effectively abolish their inhibitory effects. These differences are attributed to distinct voltage-dependence and kinetic characteristics regarding the dissociation of the compounds from depolarized channels and their re-association with channels in the resting state. Suzetrigine requires the strongest depolarization to relieve inhibition, and the relief process is slow; consequently, negligible relief occurs during a single AP waveform. A-887826 requires less intense depolarization and acts much faster, leading to partial relief of inhibition during each AP waveform and a cumulative effect during 20 Hz train firing. LTGO-33 requires the least intense depolarization and acts even faster than A-887826, but it re-establishes inhibition much more rapidly during the intervals between AP waveforms, preventing the accumulation of relief effects during 20 Hz AP train firing. These results indicate that, unlike A-887826, neither Suzetrigine nor LTGO-33 exhibits use-dependent relief of inhibition under physiological temperatures and voltage waveforms, albeit for different reasons.

To investigate how repetitive action potential waveforms influence state-dependent inhibition under physiological conditions, researchers conducted voltage-clamp experiments at physiological temperature (37°C). They used an action potential waveform-previously recorded at 37°C from a human dorsal root ganglion (DRG) neuron-as the voltage command to record sodium currents generated by human Nav1.8 stable cell lines. The source neuron was capsaicin-sensitive, and its action potential exhibited the broad "shoulder" characteristic typical of C-fiber nociceptors. In the voltage-clamp recordings, this waveform elicited Nav1.8 currents characterized by two distinct phases (Figures 1A, C, and E): an initial rapid current during the action potential's upstroke, followed by a drop in current (corresponding to the reduced driving force for sodium at the action potential peak), and finally a plateau-like current during the action potential shoulder. The activation pattern of Nav1.8 currents during the upstroke and shoulder phases closely resembled that of TTX-resistant sodium currents previously recorded during action potentials in capsaicin-sensitive rat DRG neurons at 22°C; this indicates that, just as in rat neurons (at room temperature), human Nav1.8 channels contribute to the formation of the rapid upstroke and broad shoulder of the action potential in human nociceptors at physiological temperature.

Figure 1. Test for reverse use dependence using an AP waveform recorded from a human DRG neuron at 37°C, delivered at 20 Hz. (Jo S, et al., 2025)