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Scorpion venom is a mixture of various active substances, but generally the neurotoxins are the most important. The venom of C. sculpturatus contains a peptide neurotoxin that opens Na+-channels (b -toxin). Sodium is primarily an extracellular ion, and is necessary inter alia for maintaining an electrical voltage difference across the cell membrane. When the channels open, sodium flows into the cell and depolarises the membrane. The venom causes depolarisation, the action potentials grow longer and the nerves fire non-stop. Other components in the venom inhibit the deactivation of Na+-channels (a -toxins) and thus have a similar clinical effect. However, little of the venom can penetrate the blood-brain barrier. Apparently there are components which have an effect on the central nervous system, with bulbar impairment, but these have not yet been adequately described. There follows a massive release of neurotransmitters, both acetylcholine and noradrenaline from nerve endings and adrenaline from the adrenal medulla. The main part is formed by the catecholamines. Another component in the venom (charybdotoxine) blocks K+-channels. This molecule is very similar to the venom of Conus shells. The venom of Leiurus sp. includes chlorotoxin, which specifically acts on Cl--channels. Chlorotoxin binds specifically to receptors on cerebral glioma cells and is being studied in experimental braincancer therapy. [
Primary brain tumors (gliomas) have the unusual ability to diffusely infiltrate the normal brain thereby evading surgical treatment. Chlorotoxin is a scorpion toxin that specifically binds to the surface of glioma cells and impairs their ability to invade.] Scorpion venom also contains serotonin, which contributes to local pain. Serotonin might be responsible for triggering uterine contractions and causing miscarriages in women who are in an early stage of pregnancy when they are stung. The venom of Tityus sp. includes a kallikrein inhibitor. The venom of most scorpion species has not yet been studied. Scorpions can be electrically "milked" to obtain venom. The extent to which the composition of venom obtained in this way differs from the natural product is a subject of research.*
Note: Scorpion venom and ion channels in nerves
On a neuron´s cell membrane there are various forces at work which, at rest, are in dynamic equilibrium. At rest the cytoplasmatic side is negatively charged vis-à-vis the outside. There is an electrical gradient of 70 mV which attempts to move ions from an area with high charge density to an area of low charge density.
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Several ions show a concentration gradient. The concentrations of Na+ and K+ ions on the opposite sides of the membrane differ widely. There is a high potassium concentration inside the cell, while outside the cell this concentration is low. The opposite is true for the sodium concentrations. There is thus both an electrical and a chemical gradient. There is a sodium-potassium pump in the nerve membrane. For every three sodium ions that are pumped out, two potassium ions are brought into the cell. Many potassium ions leak out of the cell, which further increases the negative charge of the interior of the membrane. The nerve cells also have various ion channels, including sodium channels which are opened when there is a specific electrical voltage (voltage-gated channels). It is these channels which are permanently opened by scorpion venom.
