Editing Saxitoxin (section)

==Mechanism of action==
{{Main|Sodium channel blocker}}
[[File:Neurotoxin Sodium Channel Binding Sites.png|thumb|A diagram of the membrane topology of a voltage gated sodium channel protein. Binding sites for different neurotoxins are indicated by color. Saxitoxin is denoted by red.]]

Saxitoxin is a neurotoxin that acts as a [[Binding selectivity|selective]], reversible, [[Voltage-gated ion channel|voltage-gated]] [[sodium channel blocker]].<ref>{{Cite book|title=Handbook of toxicology of chemical warfare agents|publisher=Academic Press|others=Gupta, Ramesh C. (Ramesh Chandra), 1949-|date=21 January 2015|isbn=978-0-12-800494-4|edition=Second|location=London|pages=426|oclc=903965588}}</ref><ref name="pmid2542373">{{Cite journal | last1 = Huot | first1 = R. I. | last2 = Armstrong | first2 = D. L. | last3 = Chanh | first3 = T. C. | doi = 10.1172/JCI114087 | title = Protection against nerve toxicity by monoclonal antibodies to the sodium channel blocker tetrodotoxin | journal = Journal of Clinical Investigation | volume = 83 | issue = 6 | pages = 1821–1826 | date=June 1989| pmid = 2542373| pmc =303901 }}</ref> One of the most [[Potency (pharmacology)|potent]] known natural toxins, it acts on the voltage-gated sodium channels of [[neurons]], preventing normal cellular function and leading to [[paralysis]].<ref name="sax"/>

The voltage-gated sodium channel is essential for normal neuronal functioning. It exists as [[integral membrane protein]]s interspersed along the [[axon]] of a neuron and possessing four [[Protein domain|domains]] that span the [[cell membrane]]. Opening of the voltage-gated sodium channel occurs when there is a change in [[voltage]] or some [[ligand]] binds in the right way. It is of foremost importance for these sodium channels to function properly, as they are essential for the propagation of an [[action potential]]. Without this ability, the nerve cell becomes unable to transmit signals and the region of the body that it enervates is cut off from the [[nervous system]]. This may lead to paralysis of the affected region, as in the case of saxitoxin.<ref name="sax"/>

Saxitoxin binds reversibly to the sodium channel. It binds directly in the pore of the channel protein, occluding the opening, and preventing the flow of sodium ions through the membrane. This leads to the nervous shutdown described above.<ref name="sax"/>