As mentioned in the key terms page, tetrodotoxin is a neurotoxin that blocks fast, voltage-gated sodium channels [5]. These channels are vital to signal transduction in neurons. Without these ion channels, you could not coordinate any muscle contraction, have any organized thought, or really do much of anything. This is why it is considered one of the most lethal neurotoxins known to man[8]. The page on tetrodotoxin in human elaborates on human tolerance of TTX, but really you wouldn’t want too many, let alone any, of your fast acting sodium channels blocked.
TTX blocks these channels like a key in a lock. The shape of the toxin fits perfectly to impede any possible ion flow. The channel is made up of four repeating subunits (see figure below), that usually allow a Na+H2O ionic molecule through. However, TTX tightly bond to the channel, and does not let any ions pass (see figure below).
Image of the repeating subunit of the ion channel, and how it is spatially arranged, as viewed from outside the cell. Images courtesy of http://www.life.umd.edu/grad/mlfsc/zctsim/ionchannel.html
Mechanism of TTX inhibition. Image courtesy of http://www.life.umd.edu/grad/mlfsc/zctsim/ionchannel.html
