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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 NaV1.8 (a tetrodotoxin-resistant isoform of VGSCs) and have analgesic properties. The effect of NaVβ-subunit co-expression on susceptibility to block by μO-MrVIA/B and STX has, until now, not been reported. Here, we show that β1-, β2-, β3and β4-subunits, when individually co-expressed with NaV1.8 in Xenopus oocytes, increased the kon of the block produced by μO-MrVIB (by 3, 32, 2 and 7-fold, respectively) and modestly decreased the apparent koff . Strong depolarizing pre-pulses markedly accelerated MrVIB washout with rates dependent on β-subunit co-expression. Thus, coexpression of β-subunits with NaV1.8 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 upregulated following nerve injury (Pertin et al., 2005 J Neurosci, 25: 10970); 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 NaV1.8 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. This article has not been copyedited and formatted. The final version may differ from this version. JPET Fast Forward. Published on May 17, 2011 as DOI: 10.1124/jpet.110.178343 at A PE T Jornals on M arch 0, 2017 jpet.asjournals.org D ow nladed from