Definition Circular Polarizing

Definition Circular Polarizing

Ion Channels

Ion channels are complex membrane protein and its function is to facilitate the diffusion of ions through biological membranes.

British biophysicists Alan Hodgkin and Andrew Huxley's hypothesis of the existence of ion channels as part of his Nobel Prize winning theory of the nerve impulse, published in 1952. Channel existence was confirmed in the 1970s with an electrical recording technique known as the patch clamp, "by Erwin Neher and Bert Sakmann, the inventors of the art 1. Nobel Prizes 2003 Peter agreed and Roderick MacKinnon, have been analyzed physico-chemical properties of the functions of ion channels, which are necessary for the cell to function.

Structural Features
In the 1990s the first structure of an ion channel determined at atomic resolution is 3 nm of the bacterial porins, a family of trimeric channel proteins homo. Each subunit contains 16 to 18 transmembrane anti-parallel beta-strands forming a beta-barrel structure. The beta-strands are amphipathic, containing alternating polar and non-waste polar and the interaction between chapter is completely saturated with H-bonding. This creates an interior hydrophilic pores provide a channel filled with water. The channel 0.8×1.1nm a large diameter, and is not selective for small ions. However, it has superior size exclusion limit corresponding to a molecular weight of approximately K 6 Da. Most of the metabolites have a molecular weight lower than 6 kDa and has been shown to pass through porin channels.

Mode of action
A ion channel is an integral membrane protein, or more often a set of proteins. These "multi-subunit" assemblies usually involve a provision circular identical or related proteins tightly around a water-filled pore through the plane of the membrane or lipid bilayer. While large-pore channels permit the passage of ions more or less indiscriminately, the archetypal channel pore is only one or two atoms wide at its narrowest point, performs a specific species ion, such as sodium or potassium, and transported through the membrane single file – nearly as fast as the ions move through the free liquid. Access to pores is governed by the "doors" that can be opened or closed by chemical or electrical signals, or mechanical force, depending on the variety of channels. There different groups of channels

– Ligand neurotransmitters closed channels

– Closed channels transmembrane voltage potential (electric field)

– Second closed channel messenger nucleotides, G-proteins

– The osmotic pressure mechanosensitive channels, the membrane curvature

– The Gap junctions not closed porins

X-ray analysis of potassium channel of Streptomyces lividans (called K1) reveals that four identical subunits create an inverted teepee, or cone, cradling the selectivity filter of the pore in its outer end. The narrow selectivity filter is only 12? long, while the rest of the pore is wider and lined with hydrophobic amino acids. A large water-filled cavity and helix dipoles are positioned so as to overcome electrostatic destabilization ion in the pore in the center of the bilayer. Main chain carbonyl oxygen atoms line K1 channel signature sequence of the selectivity filter, which remains open by structural constraints to coordinate K1 ions but not smaller ions Na1. The selectivity filter contains two K1 ions about 7.5 angstroms apart. This configuration promotes ion conduction by exploiting electrostatic repulsive forces to overcome the forces of attraction between the ions K1 and the selectivity filter. The architecture of the pore establishes the physical principles underlying selective driving K1 2.

Role in the nervous system channels are especially prominent components of the nervous system, voltage-dependent "channels leading the nerve impulse and" transmitter "closed" channels mediating conduction through the synapses. Many toxins are typically present in the channels to shut down the nervous systems of predators and prey 3.

Biological paper, ion channels figure in a wide variety of biological processes that involve rapid changes in cells, such as cardiac, skeletal, and smooth muscle contraction, epithelial transport of nutrients and ions, T cell activation and release of insulin from the pancreas of cells beta 4.

drug targets, ion channels are the main targets of many drugs already used in clinics. Most of these drugs were introduced into the therapy based on empirical experience enough, and many were discovered after targeting ion channels. The intense research underway to develop new drugs that act selectively channel subtypes onion and directed to understanding the intimate interaction with drugs channel. Polymorphisms or mutations in ion channel genes modify the sensitivity to drugs, opening the way towards the development of pharmacogenetics 5.

1.Book: Neuroscience, the ion channels underlying action potentials., For P Dale, George A, Sunderland (MA): Sinauer Associates, Inc., 2001
2.Doyle DA, Morais CJ, Pfuetzner RA, Kuo A, JM Gulbis, SL Cohen, BT Chait, R MacKinnon (1998). The structure of the potassium channel: molecular basis of K conduction and selectivity. Science, 280 (5360) :69-77.
3.Camerino DC, Tricarico D, Desaphy JF (2007). Ion channel pharmacology. Neurotherapeutics, 4 (2) :184-98.
4.Book: Chapter 6: electrical excitability and basic Ion neurochemistry: molecular, cellular and medical., For Hille B, Catterall WA. Philadelphia: Lippincott-Raven.
5.Camerino DC, Desaphy JF, Tricarico D, S Leg Liantonio A (2008). Therapeutic approaches for ion channel diseases. Adv. Genet., 64:81-145.

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