Receptor (biochemistry)

In biochemistry and pharmacology, a receptor is a protein-molecule that receives chemical-signals from outside a cell. When such chemical-signals bind to a receptor, they cause some form of cellular/tissue-response, e.g. a change in the electrical-activity of a cell. In this sense, a receptor is a protein-molecule that recognises and responds to endogenous-chemical signals, e.g. an acetylcholine-receptor recognizes and responds to its endogenous-ligand, acetylcholine. However, sometimes in pharmacology, the term is also used to include other proteins that are drug-targets, such as enzymes, transporters and ion-channels.

Receptor-proteins are embedded in all cells' plasmatic-membranes; facing extracellular-(cell surface receptors), cytoplasmic (cytoplasmic-receptors), or in the nucleus (nuclear receptors). A molecule that binds to a receptor is called a ligand, and can be a peptide (short-protein) or another small molecule such as a neurotransmitter, hormone, pharmaceutical-drug, toxin, or parts of the outside of a virus or microbe. The endogenously designated-molecule for a particular receptor is referred to as its endogenous-ligand. E.g. the endogenous-ligand for the nicotinic-acetylcholine receptor is acetylcholine but the receptor can also be activated by nicotine and blocked by curare.

Immune receptor

An immune receptor (or immunologic receptor) is a receptor, usually on a cell membrane, which binds to a substance (for example, a cytokine) and causes a response in the immune system.

Types

The main receptors in the immune system are pattern recognition receptors (PRRs), Toll-like receptors (TLRs), killer activated and killer inhibitor receptors (KARs and KIRs), complement receptors, Fc receptors, B cell receptors and T cell receptors.

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Alpha-2 adrenergic receptor

The alpha-2 (α₂) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the G_i heterotrimeric G-protein. It consists of three highly homologous subtypes, including α_2A-, α_2B-, and α_2C-adrenergic. Some species other than humans express a fourth α_2D-adrenergic receptor as well.Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α₂-adrenergic receptor in the central and peripheral nervous systems.

Cellular localisation

α_2A adrenergic receptor is localised in the following central nervous system (CNS) structures:

Whereas the α_2B adrenergic receptor is localised in the following CNS structures:

and the α_2C adrenergic receptor is localised in the CNS structures:

Extreme

Extreme or xtreme may refer to:

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Extreme (Travel Channel series)

The Extreme series on the US Travel Channel features "the absolute best of what the US of A has to offer—to the total EXTREME". Produced by Sharp Entertainment, it travels around the United States to document and showcase various places, events, things and people that are extreme in some way.

Episodes

CSI: Miami (season 2)

The second season of CSI: Miami premiered on CBS on September 22, 2003 and ended May 24, 2004. The series stars David Caruso and Emily Procter.

Cast

Starring

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