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Batrachotoxin ( BTX) is an extremely potent cardiotoxic and neurotoxic alkaloid found in certain species of beetles, birds, and frogs. The name is from the Greek word . The Merck Index. Entry 1009. p. 167. Structurally-related chemical compounds are often referred to collectively as batrachotoxins. In certain frogs, this alkaloid is present mostly on the skin. Such frogs are among those used for poisoned dart. Batrachotoxin binds to and irreversibly Channel opener the sodium channels of Neuron and prevents them from closing, resulting in paralysis and death. No antidote is known.
The toxin is released through colourless or milky secretions from glands located on the back and behind the ears of frogs from the genus Phyllobates. When one of these frogs is agitated, feels threatened or is in pain, the toxin is reflexively released through several canals.
Batrachotoxin activity is temperature-dependent, with a maximum activity at . Its activity is also more rapid at an alkaline pH, which suggests that the unprotonated form may be more active.
This has a direct effect on the peripheral nervous system (PNS). Batrachotoxin in the PNS produces increased permeability (selective and irreversible) of the resting cell membrane to sodium ions, without changing potassium or calcium concentration. This influx of sodium depolarizes the formerly polarized cell membrane. Batrachotoxin also alters the ion selectivity of the ion channel by increasing the permeability of the channel toward larger cations. Voltage-sensitive sodium channels become persistently active at the resting membrane potential. Batrachotoxin kills by permanently blocking nerve signal transmission to the muscles.
Batrachotoxin binds to and irreversibly opens the sodium channels of nerve cells and prevents them from closing. The neuron can no longer send signals and this results in paralysis. Furthermore, the massive influx of sodium ions produces osmotic alterations in nerves and muscles, which causes structural changes. It has been suggested that there may also be an effect on the central nervous system, although it is not currently known what such an effect may be.
While it is not an antidote, the membrane depolarization can be prevented or reversed by either tetrodotoxin (from puffer fish), which is a noncompetitive inhibitor, or saxitoxin. These both have effects antagonistic to those of batrachotoxin on sodium flux. Certain may act as receptor antagonists to the action of this alkaloid poison, while other block its action altogether by acting as competitive antagonists.
Several species of bird endemic to New Guinea have the toxin in their skin and on their feathers: the blue-capped ifrit ( Ifrita kowaldi), little shrikethrush (aka rufous shrike-thrush, Colluricincla megarhyncha), and the following pitohui species: the hooded pitohui ( Pitohui dichrous, the most toxic of the birds), crested pitohui ( Ornorectes cristatus), black pitohui ( Melanorectes nigrescens), rusty pitohui ( Pseudorectes ferrugineus), and the variable pitohui, which is now split into three species: the northern variable pitohui ( Pitohui kirhocephalus), Raja Ampat pitohui ( P. cerviniventris), and southern variable pitohui ( P. uropygialis).
While the purpose for toxicity in these birds is not certain, the presence of batrachotoxins in these species is an example of convergent evolution. It is believed that these birds gain the toxin from batrachotoxin-containing insects that they eat and then secrete it through the skin.
Batrachotoxin has also been found in all described species of the poison dart frog genus Phyllobates from Nicaragua to Colombia, including the golden poison frog ( Phyllobates terribilis), black-legged poison frog ( P. bicolor), lovely poison frog ( P. lugubris), Golfodulcean poison frog ( P. vittatus), and Kokoe poison frog ( P. aurotaenia). The Kokoe poison frog used to include P. sp. aff. aurotaenia, now recognized as distinct. All six of these frog species are in the poison dart frog family.
The frogs do not produce batrachotoxin themselves. Just as in the birds, it is believed that these frogs gain the toxin from batrachotoxin-containing insects that they eat, and then secrete it through the skin. Beetles in the genus Choresine are not found in Colombia, but it is thought that the frogs might get the toxin from beetles in other genera within the same family (Melyridae), several of which are found in Colombia.
Frogs raised in captivity do not produce batrachotoxin, and thus may be handled without risk. However, this limits the amount of batrachotoxin available for research as 10,000 frogs yielded only 180 mg of batrachotoxin.Du Bois, Justin, et al., inventor; Board of Trustees of the Leland Stanford Junior University, assignee. Batrachotoxin Analogues, Compositions, Uses, and Preparation Thereof. US patent 2014/0171410 A1. June 19, 2014. As these frogs are endangered, their harvest is Ethics. Biosynthetic studies are also challenged by the slow rate of synthesis of batrachotoxin.
The native habitat of poison dart frogs is the warm regions of Central America and South America.
Poison darts are prepared by the Chocó by first impaling a frog on a piece of wood. By some accounts, the frog is then held over or roasted alive over a fire until it cries in pain. Bubbles of poison form as the frog's skin begins to blister. The dart tips are prepared by touching them to the toxin, or the toxin can be caught in a container and allowed to ferment. Poison darts made from either fresh or fermented batrachotoxin are enough to drop monkeys and birds in their tracks. Nerve paralysis is almost instantaneous. Other accounts say that a stick siurukida ("bamboo tooth") is put through the mouth of the frog and passed out through one of its hind legs. This causes the frog to Perspiration profusely on its back, which becomes covered with a white froth. The darts are dipped or rolled in the froth, preserving their lethal power for up to a year.
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