Hapalochlaena lunulata

About the Toxin 

All organisms have grown and changed and adapted over time.  Plants gained a waxy cuticle to keep from drying out, flu viruses change from year to year as they become immune to vaccines, and the greater blue-ringed octopus contains a neurotoxin called tetrodotoxin to capture its prey and ward off predators. 

Tetrodotoxin chemical structureTo the left you will find a picture that I have produced of the tetrodotoxin chemical.  In most organisms, there is a homeostatic balance of sodium and potassium in the body, especially the nerve cells.  Nerve cells conduct their action potentials by depolarizing and repolarizing at specific intervals to send an action potential along the axon of the nerve cell.  During this process, there is the opening of sodium ion channels based on the electric state of the nerve cell.  When the cell begins to depolarize, positive sodium ions are rushed into the cell to maintain that homeostatic balance.  As the cell repolarizes, potassium channels open to allow the influx of those ions.  This neurotoxin, however, is shaped in a way that imitates the hydrated sodium cation and binds to a structure within the sodium channel.  With the tetrodotoxin molecules blocking the movement of actual sodium ions, the action potential within the cell slows to an eventual end.  It takes very little, about a single milligram of this lethal toxin to kill an adult human within hours.

When looking at research done by Becky Williams and Roy Caldwell at the University of California in Berkeley, one can learn that the most concentrated tetrodotoxin is found in the posterior salivary gland of Hapalochlaena lunulata.  However, the area with the highest amount of the toxin is the mantle for both the ventral and dorsal sides.  More specifically, the skin of the organism holds the most toxin due to the organ's larger mass.  One fascinating fact about the tetrodotoxin in the greater blue-ringed octopuses is that it is actually synthesized by a symbiotic bacteria found in the posterior salivary gland.  All of the specimens for the experiment were obtained in relatively the same area, yet there was considerable variation in the levels of the toxin within each individual.  Because of this, it can be determined that location has little to no effect on the amount of tetrodotoxin found in the greater blue-ringed octopuses.

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