Structure of a putative sodium channel from the sea anemone Aiptasia pallida.

A cDNA encoding a full length putative sodium channel has been cloned from the sea anemone Aiptasia pallida. The deduced protein, named AiNa1, has a predicted molecular weight of 205,000 Da. It shows high structural similarity to other sodium channels from both invertebrates and vertebrates, and its structure is consistent with the four domain, six transmembrane segment motif of all known voltage-gated sodium channels. In the region purported to constitute the tetrodotoxin (TTX) receptor of sodium channels, AiNa1 differs from the TTX-sensitive motif, suggesting that currents carried by this channel would be insensitive to TTX. The presence of a conventional sodium channel protein in anemones indicates, for the first time, that neurons in sea anemones are likely to be capable of producing fast, overshooting action potentials.