Editing Ion channel (section)

== Basic features ==
[[File:Spin 1K4C.gif|thumb|Structure of the KcsA [[potassium channel]] ([https://www.rcsb.org/3d-view/1K4C/1?preset=membrane PDB: 1K4C]). The two gray planes indicate the [[hydrocarbon]] boundaries of the [[lipid bilayer]] and were calculated with the ANVIL algorithm.<ref name="anvil">{{Cite journal|last1=Postic|first1=Guillaume|last2=Ghouzam|first2=Yassine|last3=Guiraud|first3=Vincent|last4=Gelly|first4=Jean-Christophe|date=2016|title=Membrane positioning for high- and low-resolution protein structures through a binary classification approach|journal=Protein Engineering, Design and Selection|volume=29|issue=3|pages=87–91|doi=10.1093/protein/gzv063|pmid=26685702|doi-access=free}}</ref>]]
There are two distinctive features of ion channels that differentiate them from other types of ion transporter proteins:<ref name = isbn978-0-87893-321-1 />
# The rate of ion transport through the channel is very high (often 10<sup>6</sup> ions per second or greater).
# Ions pass through channels down their [[electrochemical gradient]], which is a function of ion concentration and membrane potential, "downhill", without the input (or help) of metabolic energy (e.g. [[Adenosine triphosphate|ATP]], [[co-transport]] mechanisms, or [[active transport]] mechanisms).
Ion channels are located within the [[cell membrane|membrane]] of all excitable cells,<ref name=all/> and of many intracellular [[organelle]]s. They are often described as narrow, water-filled tunnels that allow only ions of a certain size and/or charge to pass through. This characteristic is called [[selective permeability]]. The archetypal channel pore is just one or two atoms wide at its narrowest point and is selective for specific species of ion, such as [[sodium]] or [[potassium]]. However, some channels may be permeable to the passage of more than one type of ion, typically sharing a common charge: positive ([[cation]]s) or negative ([[anion]]s). Ions often move through the segments of the channel pore in a single file nearly as quickly as the ions move through the free solution. In many ion channels, passage through the pore is governed by a "gate", which may be opened or closed in response to chemical or electrical signals, temperature, or mechanical force.{{cn|date=August 2024}}

Ion channels are [[integral membrane protein]]s, typically formed as assemblies of several individual proteins. Such "multi-[[protein subunit|subunit]]" assemblies usually involve a circular arrangement of identical or [[homology (biology)|homologous]] proteins closely packed around a water-filled pore through the plane of the membrane or [[lipid bilayer]].<ref name="isbn978-0-87893-741-7">{{cite book | editor-link1 = Dale Purves | editor-first1 = Dale | editor-last1 = Purves | editor-first2 = George J. | editor-last2 = Augustine | editor-first3 = David | editor-last3 = Fitzpatrick | editor-link4 = Larry Katz | editor-first4 = Lawrence. C. | editor-last4 = Katz | editor-first5 = Anthony-Samuel | editor-last5 = LaMantia | editor-first6 = James O. | editor-last6 = McNamara | editor-first7 = S. Mark | editor-last7 = Williams | name-list-style = vanc | title = Neuroscience | edition = 2nd | publisher = Sinauer Associates Inc. | year = 2001 | chapter = Chapter 4: Channels and Transporters | isbn = 978-0-87893-741-7 | chapter-url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=neurosci.chapter.227 }}</ref><ref name="isbn0-397-51820-X">{{cite book | author-link1=Bertil Hille  | vauthors =  Hille B, Catterall WA | editor-first1 = George J | editor-last1 = Siegel | editor-first2 = Bernard W | editor-last2 = Agranoff | editor-first3 = R. W | editor-last3 = Albers | editor-first4 = Stephen K | editor-last4 = Fisher | editor-first5 = Michael D | editor-last5 = Uhler | name-list-style = vanc | title = Basic neurochemistry: molecular, cellular, and medical aspects | publisher = Lippincott-Raven | location = Philadelphia | year = 1999 | chapter = Chapter 6: Electrical Excitability and Ion Channels| isbn = 978-0-397-51820-3 | chapter-url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=bnchm.chapter.421 }}</ref> For most [[voltage-gated ion channel]]s, the pore-forming subunit(s) are called the α subunit, while the auxiliary subunits are denoted β, γ, and so on.