| receptors, purinergic | Cell surface proteins that bind purines with high affinity and trigger intracellular changes which influence the behaviour of cells. The best characterised classes of purinergic receptors in mammals are the p1 receptors, which prefer adenosine, and the p2 receptors, which prefer ATP or ADP. (12 Dec 1998) |
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| receptors, purinergic p1 | A class of cell surface receptors that prefers adenosine to other endogenous purines. Purinergic p1 receptors are widespread in the body including the cardiovascular, respiratory, immune, and nervous systems. There are at least two pharmacologically distinguishable types (a1 and a2, or ri and ra). The methylxanthines, e.g., caffeine, bind to these receptors, but also have other unrelated effects. (12 Dec 1998) |
| receptors, purinergic p2 | A class of cell surface receptors for purines that prefer ATP or ADP over adenosine. P2 purinergic receptors are widespread in the periphery and in the central and peripheral nervous system. Subtypes have been proposed, usually designated p2 x, y, z, and t. P2x receptors may mediate fast synaptic transmission by ATP. The ADP-preferring p2t receptors in platelets stimulate aggregation. (12 Dec 1998) |
| receptors, retinoic acid | Proteins in the nucleus or cytoplasm that specifically bind retinoic acid or retinol and trigger changes in the behaviour of cells. Retinoic acid receptors, like steroid receptors, are ligand-activated transcription regulators. Several types have been recognised. (12 Dec 1998) |
| receptors, sensory | Specialised neurons or parts of neurons which transduce sensory information and relay it centrally. Included are receptors for stimuli outside the body (exteroceptors) as well as receptors for stimuli from within the body itself (interoceptors and proprioceptors). Sensory receptors may include accessory structures which condition (e.g., filter) the input received by the receptor neurons themselves. (12 Dec 1998) |
| receptors, serotonin | Cell-surface proteins that bind serotonin and trigger intracellular changes which influence the behaviour of cells. Several types of serotonin receptors have been recognised which differ in their pharmacology, molecular biology, and mode of action. (12 Dec 1998) |
| receptors, sigma | A class of cell surface receptors recognised by its pharmacological profile. Sigma receptors were originally considered to be opioid receptors because they bind certain synthetic opioids. However they also interact with a variety of other psychoactive drugs, and their endogenous ligand is not known (although they can react to certain endogenous steroids). Sigma receptors are found in the immune, endocrine, and nervous systems, and in some peripheral tissues. (12 Dec 1998) |
| receptors, somatomedin | Cell surface receptors that bind somatomedins and trigger intracellular changes which influence the behaviour of cells. Studies have disclosed two types of receptors for this family of peptide hormones. The type I receptor is homologous to the insulin receptor and has tyrosine kinase activity. The type II receptor is identical to the mannose-6-phosphate receptor which is important in trafficking of lysosomal enzymes. (12 Dec 1998) |
| receptors, somatostatin | Cell surface proteins that bind somatostatin and trigger intracellular changes which influence the behaviour of cells. Somatostatin is a hypothalamic hormone, a pancreatic hormone, and a central and peripheral neurotransmitter. Activated somatostatin receptors on pituitary cells inhibit the release of growth hormone; those on endocrine and gastrointestinal cells regulate the absorption and utilization of nutrients; and those on neurons mediate somatostatin's role as a neurotransmitter. (12 Dec 1998) |
| receptors, somatotropin | Cell surface proteins that bind somatotropin with high affinity and trigger intracellular changes influencing the behaviour of cells. Activation of growth hormone receptors regulates amino acid transport through cell membranes, RNA translation to protein, DNA transcription, and protein and amino acid catabolism in many cell types. Many of these effects are mediated indirectly through stimulation of the release of somatomedins. (12 Dec 1998) |
| receptors, steroid | Proteins found usually in the cytoplasm or nucleus that specifically bind steroid hormones and trigger changes influencing the behaviour of cells. The steroid receptor-steroid hormone complex regulates the transcription of specific genes. (12 Dec 1998) |
| receptors, tachykinin | Cell surface proteins that bind tachykinins with high affinity and trigger intracellular changes influencing the behaviour of cells. Three classes of tachykinin receptors have been characterised, the nk-1, nk-2, and nk-3, which prefer, respectively, substance p, neurokinin a (substance k, neurokinin alpha, neuromedin l), and neurokinin b (neurokinin beta, neuromedin k). (12 Dec 1998) |
| receptors, thrombin | Cell surface proteins that specifically bind thrombin and trigger changes in the behaviour of blood cells. There are at least two types of thrombin receptors on platelets. The higher affinity receptors mediate the inhibition of stimulated adenylate cyclase, the secretion of acid hydrolases, and the activation of phospholipase a2. The lower affinity receptors are linked to phospholipase c and trigger platelet aggregation and exposure of fibrinogen binding sites. A human platelet thrombin receptor has been cloned and is a member of the family of peptide receptors. There are also thrombin receptors on endothelial cells and smooth muscle cells. (12 Dec 1998) |
| receptors, thromboxane | Cell surface proteins that bind thromboxanes with high affinity and trigger intracellular changes influencing the behaviour of cells. at least a subset of thromboxane receptors act via the inositol phosphate and diacylglycerol second messenger systems. (12 Dec 1998) |
| receptors, thyroid hormone | Proteins, usually found in the nucleus, that specifically bind thyroid hormones and regulate DNA transcription. These proteins, termed c-erba, are activated by hormones and cause differentiation of erythroid progenitor cells which irreversibly lose proliferative potential. Thus c-erba proteins act as growth suppressors. The c-erba proteins are encoded by at least two genes, c-erba alpha and c-erba beta. Each of these has two isoforms. Mutations in the ligand-binding domain of the beta form causes thyroid hormone resistance syndrome. (12 Dec 1998) |