A novel μ-conopeptide, CnIIIC, exerts potent and preferential inhibition of NaV1.2/1.4 channels and blocks neuronal nicotinic acetylcholine receptors

Abstract

BACKGROUND AND PURPOSE The μ-conopeptide family is defined by its ability to block voltage-gated sodium channels (VGSCs), a property that can be used for the development of myorelaxants and analgesics. We characterized the pharmacology of a new μ-conopeptide (μ-CnIIIC) on a range of preparations and molecular targets to assess its potential as a myorelaxant. EXPERIMENTAL APPROACH μ-CnIIIC was sequenced, synthesized and characterized by its direct block of elicited twitch tension in mouse skeletal muscle and action potentials in mouse sciatic and pike olfactory nerves. μ-CnIIIC was also studied on HEK-293 cells expressing various rodent VGSCs and also on voltage-gated potassium channels and nicotinic acetylcholine receptors (nAChRs) to assess cross-interactions. Nuclear magnetic resonance (NMR) experiments were carried out for structural data. KEY RESULTS Synthetic μ-CnIIIC decreased twitch tension in mouse hemidiaphragms (IC50= 150 nM), and displayed a higher blocking effect in mouse extensor digitorum longus muscles (IC = 46 nM), compared with μ-SIIIA, μ-SmIIIA and μ-PIIIA. μ-CnIIIC blocked NaV1.4 (IC50= 1.3 nM) and NaV1.2 channels in a long-lasting manner. Cardiac NaV1.5 and DRG-specific Na V1.8 channels were not blocked at 1 μM. μ-CnIIIC also blocked the α3β2 nAChR subtype (IC50= 450 nM) and, to a lesser extent, on the α7 and α4β2 subtypes. Structure determination of μ-CnIIIC revealed some similarities to α-conotoxins acting on nAChRs. CONCLUSION AND IMPLICATIONS μ-CnIIIC potently blocked VGSCs in skeletal muscle and nerve, and hence is applicable to myorelaxation. Its atypical pharmacological profile suggests some common structural features between VGSCs and nAChR channels. © 2012 The British Pharmacological Society.