Some time ago I had Fugu, or puffer fish, a highly poisonous fish with no known antidote. Here is a picture to document the fact
Well, it could just be me in front of something that looks like fish, and I'm not going to eat it anyway, but trust me, I had it. Yes, I wanted to take the risk of dying from tetrodotoxin poisoning. After all, we live only once (very appropriate), and since I'm here, why not try it out? Also, note the smile of a sushi lover dream come true.
So, how does Fugu work ? A specialized chef prepares the puffer fish with a proper cutting process, removing all parts containing poison, and leaving only the edible ones. In particular, the liver is among the deadly parts, and is therefore removed completely. Other parts, like the meat, the fins, parts of the head, are safe to consume, all going into a rather particular dinner. Unfortunately I was not able to watch the cutting process: the chef was behind a bench (you can see him in the picture), but apparently he did a proper job, since I am still alive.
Why is puffer fish so poisonous? The culprit is a substance it accumulates, tetrodotoxin, probably obtained from diet or produced from symbiotic bacteria ingested by the fish. This molecule disrupts nerve signal transmission leading to body paralysis, starting from the lips and tongue, then the hands, then to all the rest, including the diafragm. With no control on the diafragm, the victim is unable to breathe, and dies of asphyxiation. During the whole process, which occurs in a matter of hours, the victim is fully conscious and awake, just unable to move, speak, and (in the end) breathe. This is because tetrodotoxin is not able to enter the brain, leaving its nerve tissues unscathed. Scary isn't it ? The poison is so powerful that 1 milligram (the quantity you can put on the tip of a pin) is enough to kill a human. A single pufferfish contains enough poison to kill tens of people. If you are taken early, kept breathing and get the toxin removed from your body, you can survive the poison and recover completely.
Nerve signal transmission is actuated by an exchange of sodium and potassium ions on the two different sides of the nerve cell membrane. The different ion concentration gives rise to a difference of potential, maintained at the expense of energy. There is an enzyme, known as the sodium-potassium pump, on the surface of the nerve cell membrane, with the task of keeping this unbalance by actively carrying three sodium ions outside the cell, and two potassium ions inside the cell at every cycle. The nerve cell stays "loaded and ready" to transmit the signal. When a signal transmission is triggered, sodium ions are allowed to flow back into the cell in a cascade event, trying to re-establish the equilibrium and suppress the gradient. This is made possible by another enzyme, a sodium transport channel. Tetrodotoxin binds strongly with this channel, thus preventing the sodium to enter the membrane. In some sense, it acts like a cork. Without this mechanism in place, the signal is no longer able to travel along the nerves down to the muscles, and paralysis ensues.
Is eating fugu really so dangerous? According to this site, incidents are approximately less than 100 per year, with a 10 to 50 % mortality. Most, probably all, of these cases are untrained people eating their own catch. The probability of dying from a certified, experienced Fugu chef are close to negligible, and probably your life is more in danger while driving to the restaurant.
The price for a Fugu dinner is high: 30.000 Yen (230 Euro) for a full course dinner for me and my host, and it is definitely not worth it. The consistency remembers rubber band, and the taste is basically neutral. The dinner therefore focuses on additional herbs, sauces and preparation to please your senses, with the fish as an additional, risky business. Definitely interesting once in a lifetime, as a "been there, done that" story, but for a much lower price I can have a delicious Italian meal where my taste buds really get involved the right way.