Conotoxin modulation of voltage-gated sodium channels
The rising phase of the action potential in excitable cells is mediated by voltage-gated sodium channels (VGSCs), of which there are nine mammalian subtypes with distinct tissue distribution and biophysical properties. The involvement of certain VGSC subtypes in disease states such as pain and epilepsy highlights the need for agents that modulate VGSCs in a subtype-specific manner. Conotoxins from marine snails of the Conus genus constitute a promising source of such modulators, since these peptide toxins have evolved to become selective for various membrane receptors, ion channels and transporters in excitable cells. This review covers the structure and function of three classes of conopeptides that modulate VGSCs: the pore-blocking μ-conotoxins, the δ-conotoxins which delay or inhibit VGSC inactivation, and the μO-conotoxins which inhibit VGSC Na+ conductance independent of the tetrodotoxin binding site. Some of these toxins have potential therapeutic and research applications, in particular the μO-conotoxins, which may develop into potential drug leads for the treatment of pain states.