Tetrodotoxin (TTX) found in diverse variety of animals including puffer fishes, some newts,
frogs and limited number of non-vertebrate species (6 different phyla). The saxitoxin (STX) and the
TTX are small molecules composed of 7,8,9 guanidinium and 1,2,3 guanidinium groups, respectively in
their structures. These groups provide positive charge to the molecules and are believed to interact with
negatively charged Glu755 and Asp400 residues in domain II and I of the sodium channel strongly. The
pharmacokinetic studies (absorption, distribution and accumulation) reported on Takifugu rubripes,
Takifugu pardalis, Takifugu niphobles, Takifugu vermicularis, Takifugu snyderi, etc. revealed that
higher concentration of TTX is accumulated in liver than in the skin or other tissues. Although TTX is
also accumulated in the skin of various marine species (secretory glands) and the excess of TTX are
emitted through skin which acts as a defence agent for those species. STX showed high toxicity on crab
and other animals, due to its accumulation in the tissues and resistance to the sodium channel proteins.
It concluded that TTX and STX based toxicities are developed on the species by the absorption,
distribution and accumulation of toxins in tissues. Also the ingestion of these species (marine species)
as food may allow transferring toxin to the human being.