A putative voltage-gated sodium channel α subunit (PpSCN1) from the hydrozoan jellyfish, Polyorchis penicillatus:: Structural comparisons and evolutionary considerations

Extant cnidarians are probably the simplest metazoans with discrete nervous systems and rapid, transient voltage-gated currents carried exclusively by Na(+) ions. Thus cnidarians are pivotal organisms for studying the evolution of voltage-gated Na(+) channels. We have isolated a full-length Na(+) channel alpha subunit cDNA (PpSCN1) from the hydrozoan jellyfish, Polyorchis penicillatus, that has one of the smallest known coding regions of a four domain Naf channel (1695 amino acids). Homologous residues that have a critical bearing on the selectivity filter, voltage-sensor and binding sites for tetrodotoxin and lidocaine in vertebrates and most invertebrates differ in cnidarians. PpSCN1 is not alternatively-spliced and may be the only pore-forming alpha subunit available to account for at least three electrophysioloscally distinct Na(+) currents that have been studied in P. penicillatus. (C) 1998 Academic Press.