The Excelsatoxin A‐Receptor TMEM233 Modulates Nav1.8

ABSTRACT The transmembrane protein (TMEM) 233 mediates Excelsatoxin A (ExTxA)‐induced pain by removing fast inactivation of the sodium channel Nav1.7. In contrast, TMEM233 itself seems to stabilize the inactivated state of Nav1.7. ExTxA‐induced activation of dorsal root ganglion (DRG) neurons is only partly inhibited by tetrodotoxin (TTX), possibly indicating that the TTX‐resistant sodium channel Nav1.8 is also modulated by ExTxA. To address this possibility, we performed patch clamp and calcium imaging experiments on mouse DRG neurons and on neuroblastoma ND7/23 and CHO cells expressing Nav1.8 and TMEM233. ExTxA‐induced calcium influx in DRG neurons was almost completely inhibited by TTX applied in combination with the selective Nav1.8‐inhibitor suzetrigine (VX‐548). ExTxA removed fast inactivation of TTX‐resistant sodium currents in DRG neurons, as well as of recombinant human or rat Nav1.8 channels co‐expressed with TMEM233 in ND7/23 or CHO cells. The co‐expression of Nav1.8 and TMEM233 was associated with an ExTxA‐independent hyperpolarizing shift of the voltage‐dependencies of fast and slow inactivation, an impeded recovery from fast inactivation and an increased use‐dependent inhibition by the local anesthetic lidocaine. These effects were constant across physiological temperatures (~10°C, 21°C and 37°C), and TMEM233 also modulated temperature‐dependent properties of Nav1.8. Our data suggest that ExTxA‐induced pain is likely to involve a TMEM233‐mediated regulation of Nav1.8. Furthermore, TMEM233 seems to be a relevant interacting protein of Nav1.8 that modulates the channel's distinct functional and pharmacological properties. These data warrant further investigations into how TMEM233 regulates nociceptor excitability.