Heterologous expression and functional analysis of rat Nav1.8 (SNS) voltage-gated sodium channels in the dorsal root ganglion neuroblastoma cell line ND7-23

The voltage-gated sodium channel Na(v)1.8 (SNS, PN3) is thought to be a molecular correlate of the dorsal root ganglion (DRG) tetrodotoxin resistant (TTX-R) Na+ current. TTX-R/Na(v)1.8 is an attractive therapeutic drug target for inflammatory and neuropathic pain on the basis of its specific distribution in sensory neurones and its modulation by inflammatory mediators. However, detailed analysis of recombinant Na(v)1.8 has been hampered by difficulties in stably expressing the functional protein in mammalian cells. Here, we show stable expression and functional analysis of rat Na(v)1.8 (rNa(v)1.8) in the rat DRG/mouse N18Tg2 neuroblastoma hybridoma cell line ND7-23. Rat Na(v)1.8 Na+ currents were recorded (789 +/- 89 pA, n = 62, over 20-cell passages) that qualitatively resembled DRG TTX-R in terms of gating kinetics and voltage-dependence of activation and inactivation. The local anaesthetic drug tetracaine produced tonic inhibition of rNa(v)1.8 (mean IC50 value 12.5 muM) and in repeated gating paradigms (2-10 Hz) also showed frequency-dependent block. There was a correlation between the ability of several analogues of the anticonvulsant/analgesic compound lamotrigine to inhibit TTX-R and rNa(v)1.8 (r = 0.72, P < 0.001). RT-PCR analysis of wild type ND7-23 cells revealed endogenous expression of the beta 1 and beta 3 accessory Na+ channel subunits-the possibility that the presence of these subunits assists and stabilises expression of rNa(v)1.8 is discussed. We conclude that the neuroblastoma ND7-23 cell line is a suitable heterologous expression system for rNa(v)1.8 Na+ channels in that it allows stable expression of a channel with biophysical properties that closely resemble the native TTX-R currents in DRG neurones. This reagent will prove Useful in the search for pharmacological inhibitors of rNa(v)1.8 as novel analgesics. (C) 2003 Elsevier Ltd. All rights reserved.