The neuromuscular sodium currents of early invertebrates such as
platyhelminths display distinctive kinetic and pharmacological properties.
We have cloned a cDNA from the horseshoe crab flatworm Bdelloura candida
that encodes a
protein homologous to the primary subunit of voltage-gated sodium channels.
The
B. candida protein, named BdNa1,
exhibits amino acid identity of 40–47% to sodium channels of vertebrates
and higher invertebrates. BdNa1 has the
multidomain structure characteristic of sodium channels, and is most
highly conserved in the hydrophobic transmembrane
segments and the regions that form the pore of the channel. Northern blot
analysis confirms the presence of a 5·4 kb
BdNa1 transcript in B. candida tissue. The information provided
by analysis of the BdNa1 sequence offers insight into
the physiology of platyhelminth sodium currents.