Narrowing in on the Target: A Pharmacological Approach to Confirming the Molecular Target of Cone Snail Neuroexcitatory Peptides
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Neuroexcitatory peptides (NEX) in the A-superfamily of peptides in the venom of fish-hunting cone snails are known to cause tetanic paralysis (spastic movements due to overstimulation of neurons). The precise mechanism by which NEX peptides cause tetanic paralysis and their molecular target remains unknown. One prevalent NEX peptide in the prey-injected venom of Conus catus is c4a, which is similar in sequence and mass to another NEX peptide of C. catus, c4e. Based on previous research done in our lab, we hypothesized that a possible molecular target for NEX peptides is the persistent sodium current. In this study we used a spinal motility assay of larval zebrafish, Danio rerio , to compare the physiological effects of our NEX peptides with pharmacological reagents. We tested two pharmacological reagents: SKA-31, an activator of certain types of Ca2+-activated K+ channels and veratridine, which activates persistent-like sodium currents. Our data showed that at high doses SKA-31 interferes with the stimulation of the CPG and antagonizes the effect of c4a/e in zebrafish larva. This is notable because the activation of Ca2+-activated K+ channels interferes with the persistent sodium current. Our data also shows that veratridine induces low levels of c4a/e-like spastic activity at a very high dose suggesting different selectivities of veratridine and c4a/e for their targets. Veratridine is the first neuroexcitatory molecule, beside c4a/e, to induce motility in our assay. This helps to strengthen our hypothesis that NEX peptides, like c4a/e, target the persistent sodium current.