PhTx-2 is a toxic fraction of the venom of the Brazilian wandering spider ''
Phoneutria nigriventer
''Phoneutria nigriventer'' is a species of medically-significant spider in the family Ctenidae, found in the Southern Cone of South America (Brazil, Uruguay, Paraguay, and Argentina). Along with other members of the genus, they are often referre ...
''.
Target
This fraction is responsible for most of the venom's effects, acts on
voltage-gated ion channels
Voltage-gated ion channels are a class of transmembrane proteins that form ion channels that are activated by changes in a cell's electrical membrane potential near the channel. The membrane potential alters the conformation of the channel prot ...
, this fraction is composed of nine different
peptides
Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Dalton (unit), Da or more are called proteins. Chains of fewer t ...
, of which PhTx-2-5 and PhTx-2-6 activate voltage-gated ion channels. PhTx-2 has been shown to be related to the activation and delay of inactivation of neuronal sodium channels, leading to an increase in the concentration of neuronal Ca++ and the release of
glutamate
Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...
, resulting in the release of
neurotransmitters
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell.
Neurotransmitters are rele ...
such as
acetylcholine
Acetylcholine (ACh) is an organic compound that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Par ...
and
catecholamines
A catecholamine (; abbreviated CA), most typically a 3,4-dihydroxyphenethylamine, is a monoamine neurotransmitter, an organic compound that has a catechol (benzene with two hydroxyl side groups next to each other) and a side-chain amine.
...
.
[{{Cite book, last1=Weiss, first1=Marcelo Barros, url=https://books.google.com/books?id=NzlyDwAAQBAJ&q=PhTx-2+convuls%C3%B5es+paralisias&pg=PT161, title=Acidentes com Animais Peçonhentos, last2=Paiva, first2=Jorge Wilson Souza, date=2018-10-10, publisher=Thieme Revinter Publicações LTDA, isbn=978-85-5465-084-1, language=pt-BR] Primates
Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers and simians ( monkeys and apes). Primates arose 74–63 ...
are more sensitive to the PhTx-1 & 2 components than in the case of
mice
A mouse (: mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
, about 4 to 5 times more sensitive. The LD50 for a 70kg adult human is 6.3 mg, but the spider has only 1-2 mg and usually delivers 0.4 mg.
References
Toxicology