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.

  • 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

    • For example, by affecting the enzyme acetylcholinesterase the receptor ligand is degraded.
    • 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 an 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.

  • Cholinergic Neurons and Receptors

    • When acetylcholine binds to acetylcholine receptors on skeletal muscle fibers, it opens ligand-gated sodium channels in the cell 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.

  • Postsynaptic Potentials and Their Integration at the Synapse

    • Many postsynaptic membrane receptors at chemical synapses are specialized to open ion channels.
    • The neurotransmitters bind to receptors on the postsynaptic terminal resulting in an opening of ion channels.
    • Unlike the action potential in axonal membranes, chemically-gated ion channels open on postsynaptic membranes.
    • When the opening of the ion channels results in a net gain of negative charge, the potential moves further from zero and is referred to as hyperpolarization.

  • Membrane Potentials as Signals

    • Ion transporter/pump proteins actively push ions across the membrane to establish concentration gradients across the membrane, and ion channels allow ions to move across the membrane down those concentration gradients, a process known as facilitated diffusion.
    • Signals are generated by opening or closing of ion channels at one point in the membrane, producing a local change in the membrane potential that causes electric current to flow rapidly to other points in the membrane.
    • The opening and closing of ion channels can induce a departure from the resting potential.
    • The changes in membrane potential can be small or larger (graded potentials) depending on how many ion channels are activated and what type they are.
    • Action potentials are generated by the activation of certain voltage-gated ion channels.

  • Hormone Receptors

    • Following an interaction with the hormones, a cascade of secondary effects within the cytoplasm of the cell is triggered, often involving the addition or removal of phosphate groups to cytoplasmic proteins, changes in ion channel permeability, or an increase in the concentrations of intracellular molecules that may act as secondary messengers, such as cyclic AMP.
    • In the absence of a ligand, the TR is bound to a corepressor protein.
    • Ligand binding to the TR causes a dissociation of co-repressor and recruitment of co-activator proteins, which in turn recruit additional proteins (such as RNA polymerase) that are responsible for the transcription of downstream DNA into RNA, and eventually into protein that results in a change in cell function.

  • Adrenergic Neurons and Receptors

    • Adrenaline or noradrenaline are receptor ligands to α1, α2, or β-adrenergic receptors (the pathway is shown in the following diagram).
    • The former interacts with calcium channels of the endoplasmic and sarcoplasmic reticulum, thus changing the calcium content in a cell.
    • Adrenaline and noradrenaline are ligands to α1, α2, or β-adrenergic receptors. α1-receptors couple to Gq, resulting in increased intracellular Ca2+ and causing smooth muscle contraction. α2 receptors couple to Gi, causing a decrease in cAMP activity and resulting in smooth muscle contraction. β-receptors couple to Gs, increasing intracellular cAMP activity and resulting in heart muscle contraction, smooth muscle relaxation, and glycogenolysis.

  • Erectile Dysfunction and the Blue Pill

    • There are various circulatory causes, including alteration of the voltage-gated potassium channel, as in arsenic poisoning from drinking water.