Receptor superfamilies subtypes

GABAa receptors are chloride channels and members of a superfamily of ligand-gated ion channel receptors 293 A family of pentameric GABAA-receptor protein subtypes exists 294 The GABAa receptor is the major molecular target for the action of many drugs in the brain 296... 

In the sympathetic part of the peripheral autonomic nervous system the simation is less complicated since only the sympathetically innervated visceral organs have receptors sensitive to the transmitter of the postganglionic sympathetic neuron noradrenaline. However, the noradrenaline sensitive receptors, which all belong to the G-protein coupled receptor superfamily, can be subdivided in at least three subtypes ai-, a - and jSi-adrenoceptors. These receptors are to a similar extent sensitive to adrenaline, a humoral transmitter which is released under sympathetic control from the adrenal medulla. Adrenaline, in contrast to noradrenaline has affinity to a forth type, the /32-adrenoceptor. In general drug interacting with the autonomous nervous system can be subdivided according to their mechanism of action. 

As mentioned above, the receptors which are sensitive to catecholamines are the so-called adrenoceptors. At least five major subtypes are present and of physiological relevance the a - (pharmacologically subdivided in a A, and ofio), 0(2- (pharmacologically subdivided in o 2A, oi2B and af2c) p2 and y03-adrenoceptor subtypes, which all belong to the G-protein coupled receptor superfamily. 

There are at least two ways to categorize receptors. One is based on describing all the receptors that share a common neurotransmitter. This is sometimes called pharmacological subtyping. The other organizational scheme for receptors is to classify them according to their common structural features and molecular interactions, a classification sometimes called receptor superfamilies. 

Receptor Superfamily Original Subtypes Present Subtypes... 

Subtypes of adenosine receptors exist - A, Aj and A3 -which have differential sensitivities to adenosine nucleoside analogues, including 2-methylthio-AMP, 2-thioadenosine, DPMA. IB-MECA, NECA, CPA. CCPA and DPCPX. These receptors, and subtypes within A2, have all been cloned. They have structures typical of the seven-transmembrane G-protein-coupled superfamily of receptors, but have amongst the shortest sequences known (A3 has only 318 amino acids), and a lack of sequence similarity with any other receptors appears to put them in a class of their own. Adenosine receptors are not sensitive to nucleotides such as ADP (adenosine diphosphate) and ATP (adenosine triphosphate), which instead act as P2 receptor agonists that are nucleotide-... 

PR, AR, GR, MR), thyroid hormone (TRa and j8), and retinoid (RARot, jS, and 7, and RXRa) receptor superfamily of nuclear transcriptional factors (207-210), multiple members of the interleukin cytokine receptor family (211), and subtypes of the glutamate (212) and adenosine (213)receptor families. The importance of access to human cloned receptors continues to be underscored as receptor binding plays an increasingly critical role in modern drug discovery (214). 

The understanding of the mechanism by which retinoids modulate gene expression implies that retinoids activate a signal-transduction pathway in which nuclear-retinoid receptors, which are members of the steroid hormone-receptor superfamily, play a pivotal role (14,16,18-22). Like other members of this family, the retinoid receptors are ligand-activated, DNA-binding transacting, transcription-modulating proteins. Two types of receptor have been identified retinoic acid receptors (RARs) and retinoid X receptors (RXRs) each type includes three subtypes of RAR (a, p, and y) and of RXR (a, P, and y) with distinct ammo- and carboxy-terminal domains. RXR-RAR... 

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