Posted by Cone snail shells are beautiful, but their venom is a potent cocktail used to paralyze passing fish. The venom is a witch’s brew of hundreds of novel compounds, many more than are found in snake venom (which has been used by science extensively as well). One compound in particular is a pain killer many times more effective than morphine.
The venom apparatus consists of a muscular venom bulb which pushes venom from a gland down a long duct to a chitinous tooth (the pink thing). The tooth is like a little barbed harpoon, which becomes soaked in venom and jabs into prey. Venom is quickly injected. There is no antivenom.
The discovery of this venom is not really new: about 25 years ago, a scientist at the University of Utah, Phillipine-born Baldomera Olivera, isolated the molecule that had the painkilling properties in humans. It took a quarter of a century to produce a synthetic version of the compound, which serves as the basis of the new drug Prialt (ziconotide).
Prialt is designed to treat the most serious, persistent pain which often accompanies conditions like cancer; specifically it is aimed at treating patients who have become resistant tolerant to morphine therapy. Prialt is 1,000 more potent than morphine, but surprisingly, it is not addictive.
Prialt blocks N-type calcium channels which play a role in the transmission of pain, and mimics the action of the w-conotoxin found in the cone snail venom (see chart below for the known neurotoxic peptides in the venom, and their actions. It is designed to be delivered directly into the cerebrospinal fluid by means of a small pump.
An interesting side note: cone snails have the world’s fasting mutating genes. The genes which encode the snail’s venom mutate at a rate that is 5 times faster than the highest mutation rate known in mammals. It is hypothesized that this rapid mutation rate allowed for the development of diverse venomous compounds which target several specific ion channels and receptors.
How is the venom, uh, collected from the snail? In snakes and other venomous creatures, this process of getting the venom is called “milking.” In the cone snail, the venom can either be extracted from the venom gland after the snail is dead or while the snail is alive. As Dr. Bingham (a collaborator with the initial discoverer of the venom) from Clarkson University said,
“The problem with the first way is that there are many compounds in the snails’ venom glands that are not actually injected into prey to paralyze and kill it. So you must sift through thousands of compounds that are unlikely to be useful. The problem with the second way is that while it is far more efficient, it is not easy to milk a highly poisonous snail.”
One last thought: I haven’t been able to determine whether the pain-relieving qualities of the venom, which are potent in humans, have the same effect in the snails prey (fish and mollusks). Initially, it seems intriguing that venom would have evolved to so, uh, merciful. However reducing pain in the snail’s prey may have had the effect of reducing struggling and making it more likely the snail will get to eat the prey before another fish does. This might really come in handy if the pain relief was instantaneous while the paralysis neuropeptide was a bit slower acting. The prey may be discouraged from initially reacting to the pain of the sting, allowing time for the crucial paralysis effects to occur. (Just a guess….)
August 9, 2007
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