Receptor

In cell biology, a structure on the surface of a cell (or inside a cell) that selectively receives and binds a specific substance. There are hoards of receptors. There are receptors for insulin, receptors for low-density lipoproteins (LDL), etc. To take an example, the receptor for substance P, a molecule that acts as a messenger for the sensation of pain, is a unique harbor on the cell surface where substance P docks. Without this receptor, substance P cannot dock and cannot deliver its message of pain. Variant forms of nuclear hormone receptors mediate processes such as cholesterol metabolism and fatty acid production. Some hormone receptors are implicated in diseases such as diabetes and certain types of cancer. A receptor called PXR appears to jump-start the body's response to unfamiliar chemicals and may be involved in drug-drug interactions. In neurology, however, a receptor may have quite a different meaning. It may refer to the terminal of a sensory nerve that receives and responds to stimuli.

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1. A structural protein molecule on the cell surface or within the cytoplasm that binds to a specific factor, such as a drug, hormone, antigen, or neurotransmitter. 2. C. Sherrington term for any one of the various sensory nerve endings in the skin, deep tissues, viscera, and special sense organs. [L. receiver, fr. recipio, to receive]

- adrenergic receptors reactive components of effector tissues, most of which are innervated by adrenergic postganglionic fibers of the sympathetic nervous system. Such receptors can be activated by norepinephrine and/or epinephrine and by various adrenergic drugs; r. activation results in a change in effector tissue function, such as contraction of arteriolar muscles or relaxation of bronchial muscles; adrenergic receptors are divided into α-receptors and β-receptors, on the basis of their response to various adrenergic activating and blocking agents. SYN: adrenoceptor, adrenoreceptors.

- α-adrenergic receptors adrenergic receptors in effector tissues capable of selective activation and blockade by drugs; conceptually derived from the ability of certain agents, such as phenoxybenzamine, to block only some adrenergic receptors and of other agents, such as methoxamine, to activate only the same adrenergic receptors. Such receptors are designated as α-receptors. Their activation results in physiologic responses such as increased peripheral vascular resistance, mydriasis, and contraction of pilomotor muscles.

- β-adrenergic receptors adrenergic receptors in effector tissues capable of selective activation and blockade by drugs; conceptually derived from the ability of certain agents, such as propranolol, to block only some adrenergic receptors and of other agents, such as isoproterenol, to activate only the same adrenergic receptors. Such receptors are designated as β-receptors. Their activation results in physiologic responses such as increases in cardiac rate and force of contraction (β₁), and relaxation of bronchial and vascular smooth muscle (β₂) contained in skeletal muscle.

- AMPA r. a type of glutamate r. that participates in excitatory neurotransmission and also binds α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid and acts as a cation channel. SYN: quisqualate r..

- angiotensin r. cell-surface G-protein–coupled receptors that mediate the effects of angiotensin II. Two types are recognized: AT₁ and AT₂; the former mediates the powerful vascular smooth-muscle contraction responsible for the hypertensive response produced by angiotensin II; the latter is not sufficiently understood to be assigned any physiologic function.

- ANP receptors cell surface receptors for atrial natriuretic peptide that have a single transmembrane spanning element; these have integral kinase and guanylate cyclase domains.

- ANP clearance receptors cell surface proteins that bind atrial natriuretic peptide and ANP fragments without initiating biologic action.

- asialoglycoprotein r. a surface r. found in hepatocytes that binds galactose-terminal glycoproteins; thus, this r. removes those proteins from circulation and they are in turn acted upon by hepatocyte lysosomes.

- B cell receptors a complex comprising a membrane-bound immunoglobulin molecule and two associated signal-transducing α and β chains.

- cholinergic receptors chemical sites in effector cells or at synapses through which acetylcholine exerts its action.

- epidermal growth factor r. (EGFR) r. often upregulated in epithelial tumors.

- estrogen r. r. for estrogens; its presence conveys a better prognosis for breast cancers.

- Fas r. See Fas.

- Fc r. receptors present on a variety of cells for the Fc fragment of immunoglobulins. These receptors recognize immunoglobulins of the IgG and IgE class.

- kainate r. a type of glutamate r. that participates in excitatory neurotransmission and also binds kainate and acts as a cation channel; injection of kainate causes death of neurons but preserves glial cells and axons.

- laminin r. a r. found in many cell types that binds laminin and has a role in cell attachment and neurite outgrowth.

- L-AP₄ r. a type of glutamate r. that also binds a particular synthetic agonist and acts as a cation channel.

- low-density lipoprotein receptors receptors on the surface of cells, especially liver cells, which bind to low-density lipoprotein and promote clearance of LDL from the plasma.

- mannose-6-phosphate receptors (MPR) receptors in Golgi apparatus to which newly synthesized proteins that are destined to enter lysosomes bind.

- metabotropic r. a type of r. that is linked to intracellular production of 1,2-diacylglycerol and inositol 1,4,5-trisphosphate. [metabolism + G. trope, turning, inclination, + -ic]

- muscarinic receptors membrane-bound proteins whose extracellular domain contains a recognition site for acetylcholine (ACh); combination of Ach with the r. initiates a physiologic change (slowing of heart rate, increased glandular secretory activity, and stimulation of smooth muscle contractions); changes are observed after treatment with the mushroom alkaloid muscarine. Muscarinic receptors are to be distinguished from nicotinic receptors.

- nicotinic receptors a class of cholinergic receptors on skeletal muscle cells that are linked to ion channels in the cell membrane.

- nicotinic cholinergic r. a class of receptors responsive to acetylcholine that also are activated by nicotine; ganglionic (including the adrenal medulla) and neuromuscular receptors. Two classes exist: nicotinic-neuronal and nicotinic-muscular.

- NMDA r. a type of glutamate r. that participates in excitatory neurotransmission and also binds N-methyl-d-aspartate; may be particularly involved in the cell damage observed in individuals with Huntington disease.

- opiate receptors regions of the brain that have the capacity to bind morphine; some, along the aqueduct of Sylvius and in the center median, are in areas related to pain, but others, as in the striatum, are not related.

- orphan r. a nuclear r. for which no ligand has yet been identified.

- progesterone r. intracellular r. for progesterone; often over-expressed in breast cancer.

- quisqualate r. SYN: AMPA r..

- retinoic acid r. nuclear r. for retinoic acid.

- retinoid X r. r. for retinoic acid s; has less affinity for retinoic acid than the retinoic acid receptors; function is not yet well understood.

- ryanodine r. r. associated with a calcium conductance channel in the sacroplasmic or endoplasmic reticulum of cells, which when bound to ryanodine, causes the channel to remain in a subconductive state, allowing slow continuing release of calcium ions from the sarcoplasmic reticulum into the cytoplasm. The channels are normally sensitive to calcium ions and not sensitive to inositol triphosphate.

- scavenger r. a r. on macrophages that binds preferentially to oxidized LDL, causing macrophages to internalize the LDL.

- sensory receptors peripheral endings of afferent neurons.

- stretch receptors receptors that are sensitive to elongation, especially those in Golgi tendon organs and muscle spindles, but also those found in visceral organs such as the stomach, small intestine, and urinary bladder; these receptors have the function of detecting elongation, and this distinguishes them from baroreceptors, which actually are activated by stretching of the wall of the blood vessel but whose function is to elicit central reflex mechanism reducing the arterial blood pressure.

- T cell antigen receptors receptors present on T cells that interact with both processed antigen and major histocompatibility antigens simultaneously; these are heterodimers, each consisting of either an α and β chain or a γ and δ chain.

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re·cep·tor ri-'sep-tər n

1) a cell or group of cells that receives stimuli: SENSE ORGAN

2) a chemical group or molecule (as a protein) on the cell surface or in the cell interior that has an affinity for a specific chemical group, molecule, or virus

3) a cellular entity (as a beta-receptor or alpha-receptor) that is a postulated intermediary between a chemical agent (as a neurohormone) acting on nervous tissue and the physiological or pharmacological response

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n.

1. a cell or group of cells specialized to detect changes in the environment and trigger impulses in the sensory nervous system. All sensory nerve endings act as receptors, whether they simply detect touch, as in the skin, or chemical substances, as in the nose and tongue, or sound or light, as in the ear and eye. See exteroceptor, interoceptor, mechanoreceptor, proprioceptor.

2. a specialized area of a cell membrane, consisting of a specially adapted protein, that can bind with a specific hormone (e.g. oestrogen receptor), neurotransmitter (e.g. adrenergic receptors), drug, or other chemical, thereby initiating a change within the cell.

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re·cep·tor (re-sepґtər) [L. recipere to receive, accept] 1. a molecular structure within a cell or on the cell surface and characterized by (1) selective binding of a specific substance and (2) a specific physiologic effect that accompanies the binding, e.g., membrane receptors for peptide hormones, neurotransmitters, antigens, complement fragments, and immunoglobulins, and nuclear receptors for steroid hormones. 2. a sensory nerve terminal that responds to stimuli of various kinds; classified in various ways including by the type of stimulus (see chemoreceptor, mechanoreceptor, photoreceptor, and thermoreceptor) and by the location in the body (see exteroceptor, interoceptor, and proprioceptor).