The discovery of a novel sodium channel in the cockroach Periplaneta americana: Evidence for an early duplication of the para-like gene

Voltage-gated sodium channels (Nav channels) belong to a superfamily of ion channels which play an essential role in membrane excitability. Only one gene encoding Nav channels has been characterized so far in insects. Here, we have cloned one full-length cDNA encoding a conventional insect Nav channel (PaNav1) and two full-length cDNAs encoding putative insect Nav channels (PaFPC1 and PaFPC2) in Periplaneta americana, a model insect for neurophysiological studies. The ORFs of PaFPC1 and PaFPC2 contained 4662 bp and encoded 1553 amino acid residues, and the ORF of PaNav1 contained 6153 bp and encoded 2051 amino acid residues. PaFPC1 and PaFPC2 are two isoforms, which differ by eight single amino acid substitutions. PaFPC1 shares 37.5-55% protein identities with known insect Nav channels, while PaNav1 shares 70-97.5% protein identities with these latter. Both PaFPC1 and PaFPC2 possess the molecular hallmarks of Nav channels except the motif involved in fast inactivation. Contrary to PaNav1 transcripts which are expressed mainly in the central nervous system, those ones of PaFPC are also expressed in non-neuronal tissues (muscles, gut and mushroom-shaped accessory glands). A detailed phylogenetic analysis confirmed that PaNav1 and PaFPC are evolutionarily closely related to insect Nav channel genes.