title: Navβ subunits modulate the inhibition of Nav1.8 by the analgesic gating modifier μO-conotoxin MrVIB.
abstract: Voltage-gated sodium channels (VGSCs) consist of a pore-forming α-subunit and regulatory β-subunits. Several families of neuroactive peptides of Conus snails target VGSCs, including μO-conotoxins and μ-conotoxins. Unlike μ-conotoxins and the guanidinium alkaloid saxitoxin (STX), which are pore blockers, μO-conotoxins MrVIA and MrVIB inhibit VGSCs by modifying channel gating. μO-MrVIA/B can block Na(v)1.8 (a tetrodotoxin-resistant isoform of VGSCs) and have analgesic properties. The effect of Na(v)β-subunit coexpression on susceptibility to block by μO-MrVIA/B and STX has, until now, not been reported. Here, we show that β1-, β2-, β3-, and β4-subunits, when individually coexpressed with Na(v)1.8 in Xenopus laevis oocytes, increased the k(on) of the block produced by μO-MrVIB (by 3-, 32-, 2-, and 7-fold, respectively) and modestly decreased the apparent k(off). Strong depolarizing prepulses markedly accelerated MrVIB washout with rates dependent on β-subunit coexpression. Thus, coexpression of β-subunits with Na(v)1.8 can strongly influence the affinity of the conopeptide for the channel. This observation is of particular interest because β-subunit expression can be dynamic, e.g., β2-expression is up-regulated after nerve injury (J Neurosci, 25:10970-10980, 2005); therefore, the effectiveness of a μO-conotoxin as a channel blocker could be enhanced by the conditions that may call for its use therapeutically. In contrast to MrVIB's action, the STX-induced block of Na(v)1.8 was only marginally, if at all, affected by coexpression of any of the β-subunits. Our results raise the possibility that μO-conotoxins and perhaps other gating modifiers may provide a means to functionally assess the β-subunit composition of VGSC complexes in neurons.
authors.affiliation: Department of Biology, University of Utah, 257 South 1400 East, Salt Lake City, UT 84112, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wilson
authors.forename: Min-Min
authors.initials: MM
authors.lastname: Zhang
authors.forename: Layla
authors.initials: L
authors.lastname: Azam
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Bulaj
authors.forename: Doju
authors.initials: D
authors.lastname: Yoshikami
mesh_terms: D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000818:Animals; D020916:Conotoxins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009865:Oocytes / Q000378:metabolism; D010452:Peptide Biosynthesis / Q000187:drug effects; D011485:Protein Binding; D021122:Protein Subunits / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000502:physiology*; D051381:Rats; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000378:metabolism* / Q000502:physiology; D014982:Xenopus laevis
chemical_list: D018712:Analgesics, Non-Narcotic; D020916:Conotoxins; D062559:NAV1.8 Voltage-Gated Sodium Channel; D021122:Protein Subunits; C568319:Scn10a protein, rat; D026941:Sodium Channel Blockers; D015222:Sodium Channels; C094741:muO-conotoxin MrVIB