Ionotropic receptors

(noun)

A group of transmembrane ion channels that open or close in response to the binding of a chemical messenger (ligand) such as a neurotransmitter.

Related Terms

  • metabotropic receptors
  • nicotinic acetylcholine receptor
  • G protein-coupled receptor
  • receptor
  • electrochemical gradient
  • ionotropic receptor

Examples of Ionotropic receptors in the following topics:

  • Ionotropic and Metabotropic Receptors

    • Although both ionotropic and metabotropic receptors are activated by neurotransmitters, ionotropic receptors are channel-linked while metabotropic receptors initiate a cascade of molecules via G-proteins.
    • Two types of membrane-bound receptors are activated with the binding of neurotransmitters: ligand-gated ion channels (LGICs) inotropic receptors and metabotropic G- protein coupled receptors.
    • Examples of metabotropic receptors include glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, most serotonin receptors, and receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides, and endocannabinoids.
    • They have a much longer effect than ionotropic receptors, which open quickly but only remain open for a few milliseconds.
    • While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread throughout the cell.
  • Ion Channels

    • A large subset function as neurotransmitter receptors—they occur at postsynaptic sites, and the chemical ligand that gates them is released by the presynaptic axon terminal.
    • Ligand-gated ion channels (LGICs) are one type of ionotropic receptor or channel-linked receptor.
  • Classification of Receptors by Stimulus

    • Sensory receptors can be classified by the type of stimulus that generates a response in the receptor.
    • Sensory receptors perform countless functions in our bodies.
    • Cutaneous receptors are sensory receptors found in the dermis or epidermis.[2]
    • Encapsulated receptors consist of the remaining types of cutaneous receptors.
    • A tonic receptor is a sensory receptor that adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that adapts rapidly to a stimulus.
  • Blocking of Hormone Receptors

    • A receptor antagonist does not provoke a biological response upon receptor binding, but limits or dampens agonist-mediated responses.
    • A receptor antagonist is a type of receptor ligand or drug that does not provoke a biological response itself upon binding to a receptor, but blocks or dampens agonist-mediated responses.
    • Binding to the active site on the receptor regulates receptor activation directly.
    • The current accepted definition of receptor antagonist is based on the receptor occupancy model.
    • Irreversible antagonists covalently bind to the receptor target and, in general, cannot be removed; inactivating the receptor for the duration of the antagonist effects is determined by the rate of receptor turnover, the rate of synthesis of new receptors.
  • Classification of Receptors by Location

    • Some sensory receptors can be classified by the physical location of the receptor.
    • Remarkably, specialized receptors have evolved to transmit sensory inputs from each of these sensory systems.
    • Receptors are sensitive to discrete stimuli and are often classified by both the systemic function and the location of the receptor.
    • Sensory receptors are found throughout our bodies, and sensory receptors that share a common location often share a common function.
    • For example, sensory receptors in the retina are almost entirely photoreceptors.
  • Types of Receptors

    • There are two types of receptors: internal receptors and cell-surface receptors.
    • Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers.
    • There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
    • Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
    • An example of this type of enzyme-linked receptor is the tyrosine kinase receptor.
  • Target Cell Specificity

    • Hormones target a limited number of cells (based on the presence of a specific receptor) as they circulate in the bloodstream.
    • This androgen insensitivity occurs when the receptors on the target cells are unable to accept the hormone due to an impairment in receptor shape.
    • Target cells are capable of responding to hormones because they display receptors to which the circulating hormone can bind.
    • Finally, hormone-receptor affinity can be altered by expression of associated inhibitory or co-activating factors.
    • In some instances alterations of receptor structure due to a genetic mutation can lead to a reduction in hormone-receptor affinity as in the case of androgen insensitivity.
  • Adrenergic Neurons and Receptors

    • Adrenergic receptors are molecules that bind catecholamines.
    • There are two main groups of adrenergic receptors, α and β, with several subtypes. α receptors have the subtypes α1 (a Gq coupled receptor) and α2 (a Gi coupled receptor).
    • Phenylephrine is a selective agonist of the α receptor. β receptors have the subtypes β1, β2 and β3.
    • α1-adrenergic receptors are members of the G protein-coupled receptor superfamily.
    • This schematic shows the mechanism of adrenergic receptors.
  • Direct Gene Activation and the Second-Messenger System

    • Hormones can alter cell activity by binding with a receptor.
    • Receptors which can directly influence gene expression are termed nuclear receptors.
    • Type I nuclear receptors are located in the cytosol.
    • Type II receptors are retained in the nucleus .
    • Most hormone receptors are G protein-coupled receptors.
  • Binding Initiates a Signaling Pathway

    • Ligand binding to cell-surface receptors activates the receptor's intracellular components setting off a signaling pathway or cascade.
    • Cell-surface receptors, also known as transmembrane receptors, are membrane-anchored (integral) proteins that bind to external ligand molecules.
    • There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
    • All G-protein-linked receptors have seven transmembrane domains, but each receptor has its own specific extracellular domain and G-protein-binding site.
    • Enzyme-linked receptors are cell-surface receptors with intracellular domains that are associated with an enzyme.
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