Journal
CHANNELS
Volume 3, Issue 1, Pages 32-38Publisher
TAYLOR & FRANCIS INC
DOI: 10.4161/chan.3.1.7500
Keywords
conotoxin; contratoxin; Na(V)1.2; oocyte; sodium channel; Site 1; syntoxin; tetrodotoxin; voltage clamp
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Funding
- National Institutes of Health [GM 48677, NS055845]
- Heart and Stroke Foundation of Alberta, Northwest Territories and Nunavut
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [P01GM048677] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [R21NS055845] Funding Source: NIH RePORTER
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Tetrodotoxin (TTX) is the quintessential ligand of voltage-gated sodium channels (Na(V)s). Like TTX, mu-conotoxin peptides are pore blockers, and both toxins have helped to define the properties of neurotoxin receptor Site 1 of NaVs. Here, we report unexpected results showing that the recently discovered mu-conotoxin KIIIA and TTX can simultaneously bind to Site 1 and act in concert. Results with saturating concentrations of peptide applied to voltage-clamped Xenopus oocytes expressing brain Na(V)1.2, and single-channel recordings from brain channels in lipid bilayers, show that KIIIA or its analog, KIIIA[K7A], block partially, with a residual current that can be completely blocked by TTX. In addition, the kinetics of block by TTX and peptide are each affected by the prior presence of the other toxin. For example, bound peptide slows subsequent binding of TTX (an antagonistic interaction) and slows TTX dissociation when both toxins are bound (a synergistic effect on block). The overall functional consequence resulting from the combined action of the toxins depends on the quantitative balance between these opposing actions. The results lead us to postulate that in the bi-liganded Na-V complex, TTX is bound between the peptide and the selectivity filter. These observations refine our view of Site 1 and open new possibilities in Na-V pharmacology.
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