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Conotoxins, which are peptides consisting of 10 to 30 amino acid residues, typically have some disulfide bonds. Conotoxins have a variety of activities, most of which have not been explained closely yet.
The number of conotoxins whose activities have been determined so far is five, and they are called the α(alpha)-, δ(delta)-, κ(kappa)-, μ(mu)-, and ω- types. Each of the five types of conotoxins attacks a different target:
- α-conotoxin attacks acetylcholine receptors at nerves and muscles.
- δ-conotoxin inhibits the inactivation of voltage-dependent sodium channels.
- κ-conotoxin inhibits potassium channels.
- μ-conotoxin inhibits voltage-dependent sodium channels in muscles.
- ω-conotoxin inhibits N-type voltage-dependent calcium channels. Because N-type voltage-dependent calcium channels are related to algesia (sensitivity to pain) in the nervous system, ω-conotoxin has an analgesic effect: the effect of ω-conotoxin M VII A is 100 to 1000 times that of morphine. Therefore ω-conotoxin M VII A is used as an analgesic drug named ziconotide; it is marketed under the brand name Prialt®.
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