A PUTATIVE VOLTAGE-GATED SODIUM-CHANNEL ALPHA-SUBUNIT (PPSCN1) FROM THE HYDROZOAN JELLYFISH, POLYORCHIS-PENICILLATUS - STRUCTURAL COMPARISONS AND EVOLUTIONARY CONSIDERATIONS

Extant cnidarians are probably the simplest metazoans with discrete ne rvous systems and rapid, transient voltage-gated currents carried excl usively by Na+ ions. Thus cnidarians are pivotal organisms for studyin g the evolution of voltage-gated Na+ channels. We have isolated a full -length Na+ channel alpha subunit cDNA (PpSCN1) from the hydrozoan jel lyfish, Polyorchis penicillatus, that has one of the smallest known co ding regions of a four domain Naf channel (1695 amino acids). Homologo us residues that have a critical bearing on the selectivity filter, vo ltage-sensor and binding sites for tetrodotoxin and lidocaine in verte brates and most invertebrates differ in cnidarians. PpSCN1 is not alte rnatively-spliced and may be the only pore-forming alpha subunit avail able to account for at least three electrophysioloscally distinct Nacurrents that have been studied in P. penicillatus. (C) 1998 Academic Press.