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Encyclopedia > Potassium channel

In cell biology, potassium channels are the most common type of ion channel. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cells, and control the electrical excitability of the cell membrane. In neurons, they shape action potentials and set the resting membrane potential. They regulate cellular processes such as the secretion of hormones, so their malfunction can lead to diseases. Cell biology (also called cellular biology or cytology, from the Greek kytos, container) is an academic discipline which studies cells. ... Another, unrelated ion channeling process is part of ion implantation. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... A pore, in general, is some form of opening, usually very small. ... Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. ... --72. ... Drawing by Santiago Ramón y Cajal of cells in the pigeon cerebellum. ... A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... The resting potential of a cell is the membrane potential that would be maintained if there were no action potentials, synaptic potentials, or other active changes in the membrane potential. ... Hormone is also the NATO reporting name for the Soviet/Russian Kamov Ka-25 military helicopter. ...


Some potassium channels are voltage-gated ion channels that open or close in response to changes in the transmembrane voltage. They can also open in response to the presence of calcium ions or other signalling molecules. Others are constitutively open or possess high basal activation, such as the resting potassium channels that set the negative membrane potential of neurons. When open, they allow potassium ions to cross the membrane at a rate which is nearly as fast as their diffusion through bulk water. There are over 80 mammalian genes that encode potassium channel subunits. The pore-forming subunits of potassium channels have a homo- or heterotetrameric arrangement. Four subunits are arranged around a central pore. All potassium channel subunits have a distinctive pore-loop structure that lines the top of the pore and is responsible for potassium selectivity. Potassium is the main intracellular ion for all types of cells. ... Voltage-gated ion channel is a ion channel that is specifically activated, or gated, by the surrounding potential difference near the channel (or near the cell, neuron or synapse). ... Membrane potential (or transmembrane potential or transmembrane potential difference or transmembrane potential gradient), is the electrical potential difference (voltage) across a cells plasma membrane. ... This article may be too technical for most readers to understand. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ... Resting channels are ion channels in the plasma membrane of a cell that remain open at all times. ... Schematic drawing of the effects of diffusion through a semipermeable membrane. ... A girl in a swimming pool full of water Water (from the Old English waeter; c. ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ... A tetramer is a protein with four subunits (tetrameric). ...


Potassium channels found in bacteria are amongst the most studied of ion channels, in terms of their molecular structure. Using X-ray crystallography, profound insights have been gained into how potassium ions pass through these channels and why (smaller) sodium ions do not (since sodium ions have greater charge density, they have a larger shell of water molecules surrounding them and thus are more bulky). The 2003 Nobel Prize for Chemistry was awarded to Rod MacKinnon for his pioneering work on this subject. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... Charge density is the amount of electric charge per unit volume. ... A girl in a swimming pool full of water Water (from the Old English waeter; c. ... In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ... 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... List of Nobel Prize laureates in Chemistry from 1901 to the present day. ... Roderick MacKinnon (born 19 February 1956 in Burlington, Massachusetts) is a professor of Molecular Neurobiology and Biophysics at Rockefeller University who in 2003 was awarded the Nobel Prize in Chemistry for his work on the structure and operation of ion channels. ...

Contents


Voltage sensitive channels

The voltage-gated K+ channels that provide the outward currents of action potentials have similarities to bacterial K+ channels. These channels have been studied by X-ray diffraction, allowing determination of structural features at atomic resolution. The function of these channels is explored by electrophysiological studies. Genetic approaches include screening for behavioral changes in animals with mutations in K+ channel genes. Such genetic methods allowed the genetic identification of the "Shaker" K+ channel gene in Drosophila before ion channel gene sequences were well known. Study of the altered properties of voltage-gated K+ channel proteins produced by mutated genes has helped reveal the functional roles of K+ channel protein domains and even individual amino acids within their structures. A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of x-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... Electrophysiology is the study of the electrical properties of biological cells and tissues. ... Type Species Musca funebris Fabricius, 1787 Species Many; see text. ...


Voltage-gated K+ channels of vertebrates typically have four protein subunits arranged as a ring, each contributing to the wall of the trans-membrane K+ pore. There are six major α-helical sequences in each subunit. Some of these are hydrophobic transmembrane sequences. A diagram of the alpha helix structure of amino acids In proteins, the α helix is a major structural motif in secondary structure. ... In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ...


Voltage-gated K+ channels are selective for K+ over other cations such as Na+. There is a selectivity filter at the narrowest part of the transmembrane pore. Channel mutation studies revealed the parts of the subunits that are essential for ion selectivity. They include the amino acid sequence (Thr-Val-Gly-Tyr-Gly) or (Thr-Val-Gly-Phe-Gly) typical to the selectivity filter of voltage-gated K+ channels. As K+ passes through the pore, interactions between potassium ions and water molecules are prevented and the K+ interacts with specific atomic components of the Thr-Val-Gly-X-Gly sequences from the four channel subunits[1]. A cation is an ion with positive charge. ... In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups. ...


Atempts continue to relate the structure of the mammalian voltage-gated K+ channel to its ability to respond to the voltage that exists across the membrane[2]. Specific domains of the channel subunits have been identified that are important for voltage-sensing and converting between the open conformation of the channel and closed conformations. There are at least two closed conformations; in one, the channel can open if the menbrane potential becomes positive inside. Voltage-gated K+ channels inactivate after opening, entering a distinctive, second closed conformation. In the inactivated conformation, the channel cannot open, even if the transmembrane voltage is favorable. A domain at one end of the K+ channel protein mediates inactivation. This end of the protein can transiently plug the inner opening of the pore, preventing ion movement through the channel.


See also

BK channels, also called MaxiK or slo channels, are large conductance Ca2+ and voltage-activated K+ channels. ... Sodium channels are integral membrane proteins that exist in a cells plasma membrane and regulate the flow of sodium (Na+) ions into it. ...

External link

  • Potassium channels - Life's Transistors

Reference


  Results from FactBites:
 
HHMI News: Visualizing a Potassium Channel (784 words)
Potassium currents in the brain, for example, underlie perception and movement, and the heart's contraction relies upon the steady ebb-and-flow of potassium.
To maintain the correct concentration of potassium, cells are equipped with pore-like proteins that poke through the cell membrane.
During the last 10 years, molecular biologists have identified many of the genes that produce the protein components of potassium channels in a variety of organisms.
Potassium channel - Wikipedia, the free encyclopedia (371 words)
Potassium channels are found in most cells and control cell function.
The pore-forming subunits of potassium channels have a homo- or heterotetrameric arrangement.
Potassium channels found in bacteria are amongst the most studied of ion channels, in terms of their molecular structure.
  More results at FactBites »

 
 

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