Electrophysiological and Pharmacological Analyses of Nav1.9 Voltage-Gated Sodium Channel by Establishing a Heterologous Expression System

Na(v)1. 9 voltage-gated sodium channel is preferentially expressed in peripheral nociceptive neurons. Recent progresses have proved its role in pain sensation, but our understanding of Na(v)1.9, in general, has lagged behind because of limitations in heterologous expression in mammal cells. In this work, functional expression of human Na(v)1.9 (hNa(v)1.9) was achieved by fusing GFP to the C-terminal of hNa(v)1.9 in ND7/23 cells, which has been proved to be a reliable method to the electrophysiological and pharmacological studies of hNa(v)1.9. By using the hNa(v)1.9 expression system, we investigated the electrophysiological properties of four mutations of hNa(v)1.9 (K419N, A582T, A842P, and F1689L), whose electrophysiological functions have not been determined yet. The four mutations significantly caused positive shift of the steady-state fast inactivation and therefore increased hNa(v)1.9 activity, consistent with the phenotype of painful peripheral neuropathy. Meanwhile, the effects of inflammatory mediators on hNa(v)1.9 were also investigated. Impressively, histamine was found for the first time to enhance hNa(v)1.9 activity, indicating its vital role in hNa(v)1.9 modulating inflammatory pain. Taken together, our research provided a useful platform for hNa(v)1.9 studies and new insight into mechanism of hNa(v)1.9 linking to pain.