ligand-gated channel

(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

Examples of ligand-gated channel in the following topics:

  • Ion Channels

    • Ligand-gated channels form another important class; these ion channels open and close in response to the binding of a ligand molecule such as a neurotransmitter.
    • There are three main types of gated channels: chemically-gated or ligand-gated channels, voltage-gated channels, and mechanically-gated channels.
    • Ligand-gated ion channels are channels whose permeability is greatly increased when some type of chemical ligand binds to the protein structure.
    • Ligand-gated channels can be activated by ligands that appear in the extracellular area or by interactions on the intracellular side.
    • Ligand-gated ion channels (LGICs) are one type of ionotropic receptor or channel-linked receptor.

  • Synaptic Transmission

    • When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated Na+ channels.
    • This depolarization causes voltage-gated Ca2+ channels to open.
    • The binding of a specific neurotransmitter causes particular ion channels, in this case ligand-gated channels, on the postsynaptic membrane to open.
    • When the presynaptic membrane is depolarized, voltage-gated Ca2+ channels open and allow Ca2+ to enter the cell.
    • The neurotransmitter diffuses across the synaptic cleft and binds to ligand-gated ion channels in the postsynaptic membrane, resulting in a localized depolarization or hyperpolarization of the postsynaptic neuron.

  • 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.
    • Ionotropic receptors are a group of transmembrane ion channels that open or close in response to the binding of a chemical messenger (ligand) such as a neurotransmitter.The binding site of endogenous ligands on LGICs protein complexes are normally located on a different portion of the protein (an allosteric binding site) than the location of the ion conduction pore.The ion channel is regulated by a ligand and is usually very selective to one or more ions such as Na+, K+, Ca2+, or Cl-.
    • The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor .
    • 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.

  • Agonists, Antagonists, and Drugs

    • ., by affecting the enzyme acetylcholinesterase, which degrades the receptor ligand.
    • Gi-protein activation also leads to the activation of KACh channels that increase potassium efflux and hyperpolarizes the cells.
    • They are ligand-gated ion channels with binding sites for acetylcholine as well as other agonists.
    • When agonists bind to a receptor it stabilizes the open state of the ion channel allowing influx of cations.
    • NAchR are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction.

  • Mechanics of the Action Potential

    • Ligand-gated ion channels: receptors that are opened or closed in response to the binding of a chemical messenger.
    • Depolarization, also referred to as the "upswing," occurs when positively charged sodium ions (Na+) suddenly rush through open sodium gates into a nerve cell.
    • The change in voltage stimulates the opening of additional sodium channels (called a voltage-gated ion channel), providing what is known as a positive feedback loop.
    • The "downswing" of repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels, resulting in the release of positively charged potassium ions (K+) from the nerve cell.
    • The sodium gates cannot be opened again until the membrane has completely repolarized to its normal resting potential, -70 mV.

  • Types of Receptors

    • Ion channel-linked receptors bind a ligand and open a channel through the membrane that allows specific ions to pass through.
    • To form a channel, this type of cell-surface receptor has an extensive membrane-spanning region.
    • When a ligand binds to the extracellular region of the channel, there is a conformational change in the protein's structure that allows ions such as sodium, calcium, magnesium, and hydrogen to pass through .
    • The activated G-protein then interacts with either an ion channel or an enzyme in the membrane.
    • Gated ion channels form a pore through the plasma membrane that opens when the signaling molecule binds.

  • Signaling Molecules

    • Important members of this class of ligands are the steroid hormones.
    • Instead, most water-soluble ligands bind to the extracellular domain of cell-surface receptors.
    • Cell-surface receptors include: ion-channel, G-protein, and enzyme-linked protein receptors.
    • The binding of these ligands to these receptors results in a series of cellular changes.
    • Nitric oxide (NO) is a gas that also acts as a ligand.

  • Binding Initiates a Signaling Pathway

    • There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors, and enzyme-linked receptors.
    • Ion channel-linked receptors bind a ligand and open a channel through the membrane that allows specific ions to pass through.
    • To form a channel, this type of cell-surface receptor has an extensive membrane-spanning region.
    • When a ligand binds to the extracellular region of the channel, there is a conformational change in the protein's structure that allows ions such as sodium, calcium, magnesium, and hydrogen to pass through.
    • The activated G-protein then interacts with either an ion channel or an enzyme in the membrane.

  • The Action Potential and Propagation

    • The depolarization, also called the rising phase, is caused when positively charged sodium ions (Na+) suddenly rush through open voltage-gated sodium channels into a neuron.
    • The repolarization or falling phase is caused by the slow closing of sodium channels and the opening of voltage-gated potassium channels.
    • As the sodium ion entry declines, the slow voltage-gated potassium channels open and potassium ions rush out of the cell.
    • Hyperpolarization is a phase where some potassium channels remain open and sodium channels reset.
    • The period from the opening of the sodium channels until the sodium channels begin to reset is called the absolute refractory period.

  • Facilitated transport

    • Similarly, a gated channel protein often remains closed, not allowing substances into the cell until it receives a signal (like the binding of an ion) to open.
    • When this signal is received, the bridge (gate) opens, allowing the boats (substance) to pass through the bridge and into the other side of the river (cell).
    • Channel proteins are either open at all times or they are "gated," which controls the opening of the channel.
    • In some tissues, sodium and chloride ions pass freely through open channels, whereas in other tissues, a gate must be opened to allow passage.
    • Cells involved in the transmission of electrical impulses, such as nerve and muscle cells, have gated channels for sodium, potassium, and calcium in their membranes.