title: Inhibitory effect of the recombinant Phoneutria nigriventer Tx1 toxin on voltage-gated sodium channels.
abstract: Phoneutria nigriventer toxin Tx1 (PnTx1, also referred to in the literature as Tx1) exerts inhibitory effect on neuronal (Na(V)1.2) 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: rNa(V)1.2 > rNa(V)1.7 ≈ rNa(V)1.4 ≥ rNa(V)1.3 > mNa(V)1.6 ≥ hNa(V)1.8. No effect was seen on hNa(V)1.5 and on the arthropods isoforms (DmNa(V)1, BGNa(V)1.1a and VdNa(V)1). The IC(50) for Na(V)1.2 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 Na(V)1.2 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.
authors.affiliation: Dept. of Biochemistry and Immunology, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais - UFMG, Av. Antonio Carlos 6627, 31270-901 Belo Horizonte, MG, Brazil.
authors.forename: Anita O
authors.initials: AO
authors.lastname: Silva
authors.forename: Steve
authors.initials: S
authors.lastname: Peigneur
authors.forename: Marcelo R V
authors.initials: MR
authors.lastname: Diniz
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
authors.forename: Paulo S L
authors.initials: PS
authors.lastname: Beirão
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001667:Binding, Competitive; D002478:Cells, Cultured; D020916:Conotoxins / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology*; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D013111:Spider Venoms / Q000378:metabolism / Q000494:pharmacology; D013779:Tetrodotoxin / Q000378:metabolism / Q000494:pharmacology; D061566:Voltage-Gated Sodium Channels / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D020916:Conotoxins; D009479:Neuropeptides; D020033:Protein Isoforms; D011994:Recombinant Proteins; D026941:Sodium Channel Blockers; D013111:Spider Venoms; C064022:Tx1 neurotoxin; D061566:Voltage-Gated Sodium Channels; D013779:Tetrodotoxin