Inhibitory effect of the recombinant Phoneutria nigriventer Tx1 toxin on voltage-gated sodium channels

Phoneutria nigriventer toxin Tx1 (PnTx1, also referred to in the literature as Tx1) exerts inhibitory effect on neuronal (NaV1.2) sodium channels in a way dependent on the holding potential, and competes with μ-conotoxins but not with tetrodotoxin for their binding sites. In the present study we investigated the electrophysiological properties of the recombinant toxin (rPnTx1), which has the complete amino acid sequence of the natural toxin with 3 additional residues: AM on the N-terminal and G on the C-terminal. At the concentration of 1.5 μM, the recombinant toxin inhibits Na+ currents of dorsal root ganglia neurons (38.4 ± 6.1% inhibition at −80 mV holding potential) and tetrodotoxin-resistant Na+ currents (26.2 ± 4.9% at the same holding potential). At −50 mV holding potential the inhibition of the total current reached 71.3 ± 2.3% with 1.5 μM rPnTx1. The selectivity of rPnTx1 was investigated on ten different isoforms of voltage-gated sodium channels expressed in Xenopus oocytes. The order of potency for rPnTx1 was: rNaV1.2 > rNaV1.7 ≈ rNaV1.4 ≥ rNaV1.3 > mNaV1.6 ≥ hNaV1.8. No effect was seen on hNaV1.5 and on the arthropods isoforms (DmNaV1, BGNaV1.1a and VdNaV1). The IC50 for NaV1.2 was 33.7 ± 2.9 nM with a maximum inhibition of 83.3 ± 1.9%. The toxin did not alter the voltage-dependence of channel gating and was effective on NaV1.2 channels devoid of inactivation. It was ineffective on neuronal calcium channels. We conclude that rPnTx1 has a promising selectivity, and that it may be a valuable model to achieve pharmacological activities of interest for the treatment of channelopathies and neuropathic pain. [Display omitted] ► rPnTx1 order of potency: rNaV1.2 > rNaV1.7 ≈ rNaV1.4 ≥ rNaV1.3 > mNaV1.6 ≥ hNaV1.8. ► The IC50 for NaV1.2 was 33.7 ± 2.9 nM. ► rPnTx1 was inactive on several arthropod NaV channel isoforms. ► Of great interest is rPnTx1 high selectivity toward Nav1.7 channels. ► rPnTx1 becomes a promising tool for the development of analgesics.