Cys-loop Receptors and Myasthenia Gravis
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Questions and Answers

What is the term for a substance that binds to a protein within the context of pharmacology?

  • Ligand (correct)
  • Receptor
  • Affinity
  • Agonist

    • Which function does an agonist perform when it binds to a receptor?

  • Binds competitively with other receptors
  • Blocks the action of other ligands
  • Inhibits receptor activity
  • Changes receptor state to elicit a biological response (correct)

    • What defines affinity in the context of a ligand and receptor interaction?

  • The total number of ligands present in a solution
  • The availability of receptor sites on a protein
  • The duration of time a ligand stays bound to a receptor
  • The strength of the bond between ligand and receptor (correct)

    • What role does an antagonist play in receptor pharmacology?

    <p>It reduces the potency of agonists at the same receptor</p> Signup and view all the answers

    In which family of receptors do Cys-loop receptors belong?

    <p>Ion channels</p> Signup and view all the answers

    What is the major autoimmune disorder associated with the loss of nicotinic acetylcholine receptors at the neuromuscular junction?

    <p>Myasthenia gravis</p> Signup and view all the answers

    Which of the following symptoms is most commonly associated with myasthenia gravis?

    <p>Muscle weakness and fatigue</p> Signup and view all the answers

    Which demographic is more commonly affected by myasthenia gravis?

    <p>Women under 40 years and men over 60 years</p> Signup and view all the answers

    Which test is commonly used for the diagnosis of myasthenia gravis?

    <p>Blood test for nAChR antibodies</p> Signup and view all the answers

    What is the duration of action for neostigmine, used in the treatment of myasthenia gravis?

    <p>1-2 hours</p> Signup and view all the answers

    What type of mutations are associated with congenital myasthenic syndrome (CMS)?

    <p>Mutations affecting nACh receptor expression and kinetics</p> Signup and view all the answers

    Which drug has the shortest duration of action among the treatments for myasthenia gravis?

    <p>Edrophonium</p> Signup and view all the answers

    What is one of the potential causes of presynaptic congenital myasthenic syndrome?

    <p>Defective ACh vesicular transport</p> Signup and view all the answers

    What are the primary ions that nicotinic acetylcholine receptors are permeable to?

    <p>Na+, K+, and Ca2+</p> Signup and view all the answers

    What role do the five subunits of the nicotinic acetylcholine receptor play?

    <p>They surround a centrally located ion channel.</p> Signup and view all the answers

    What type of channels are nicotinic acetylcholine receptors classified as?

    <p>Nonspecific cation channels</p> Signup and view all the answers

    Which organism's nicotinic acetylcholine receptor has the agonist-induced conformational change best described?

    <p>Torpedo marmorata</p> Signup and view all the answers

    Who conducted early research on the effects of nicotine on denervated skeletal muscle?

    <p>John Newport Langley</p> Signup and view all the answers

    What was the effect of applying the toxin curare in Langley's experiments?

    <p>It abolished the characteristic contractile response.</p> Signup and view all the answers

    Which statement accurately describes the ligand-binding domain of nicotinic acetylcholine receptors?

    <p>It is found between subunit interfaces.</p> Signup and view all the answers

    What physiological effect do nicotinic acetylcholine receptors primarily modulate?

    <p>Fast synaptic excitation</p> Signup and view all the answers

    What defines a channel blocker in the context of ion channels?

    <p>A molecule that binds to the pore of an ion channel and prevents ion flow</p> Signup and view all the answers

    Which of the following receptors are classified as Cys-loop receptors?

    <p>Strychnine sensitive glycine receptor and GABA-A receptors</p> Signup and view all the answers

    What is the structural composition of Cys-loop receptors?

    <p>A pentameric structure composed of five protein subunits</p> Signup and view all the answers

    How do Cys-loop receptors vary in their subunit composition?

    <p>They can be either homo-oligomers or hetero-oligomers</p> Signup and view all the answers

    What determines the pharmacology of Cys-loop receptors?

    <p>The composition of the subunits that form the receptor</p> Signup and view all the answers

    Which part of the nicotinic acetylcholine receptor is crucial for its function?

    <p>The ligand binding site at the subunit interfaces</p> Signup and view all the answers

    What is an oligomer in the context of protein structure?

    <p>A macromolecule composed of multiple protein subunits</p> Signup and view all the answers

    Which feature is NOT typically found in the structure of Cys-loop receptors?

    <p>Triple helical structure</p> Signup and view all the answers

    What role do the hydrophobic transmembrane domains serve in Cys-loop receptors?

    <p>They form the receptor's ion channel</p> Signup and view all the answers

    Which of the following receptors is NOT classified as a Cys-loop receptor?

    <p>P2X receptor</p> Signup and view all the answers

    What is the role of neurosteroids in relation to the GABAA receptor?

    <p>They directly activate the receptor at high concentrations.</p> Signup and view all the answers

    How do neurosteroids affect ion channel open-time in the GABAA receptor?

    <p>They increase the duration that the ion channel remains open.</p> Signup and view all the answers

    Which of the following conditions can alter neurosteroid levels in the brain?

    <p>Pregnancy</p> Signup and view all the answers

    What could be a potential cause of postnatal depression related to neurosteroids?

    <p>Alterations in pregnane steroid levels</p> Signup and view all the answers

    What distinguishes phasic conductance from tonic conductance?

    <p>Tonic conductance is mediated by ambient concentrations of GABA.</p> Signup and view all the answers

    Which neurotransmitter is primarily involved in the mechanisms discussed regarding neurosteroids?

    <p>GABA</p> Signup and view all the answers

    How can SSRIs impact neurosteroid levels?

    <p>They can alter neurosteroid levels in the brain.</p> Signup and view all the answers

    Which of the following is NOT a type of conductance related to GABAA receptor activity?

    <p>Sustained conductance</p> Signup and view all the answers

    What is the effect of alcohol on neurosteroid levels?

    <p>It can alter neurosteroid levels in the brain.</p> Signup and view all the answers

    In the context of neurosteroids, what does 'allosteric binding' refer to?

    <p>Binding that enhances receptor's response indirectly.</p> Signup and view all the answers

    Study Notes

    Cys-loop Receptors

    • Pentameric protein structures, composed of five protein subunits
    • Can be homo-oligomers or hetero-oligomers, with the subunit composition affecting pharmacology
    • Each subunit includes:
      • Extracellular N-terminus
      • Large intracellular loop
      • Small intracellular loop
      • Four hydrophobic transmembrane domains
      • Small extracellular loop
      • Extracellular C-terminus
    • Ligand-binding site is located between the subunit interfaces
    • Five subunits surround a centrally located ion channel

    Nicotinic Acetylcholine Receptors

    • Are nonspecific cation channels
    • Permeable to Na+, K+, and Ca2+
    • Modulate fast synaptic excitation
    • Have a key role in the neuromuscular junction

    Myasthenia Gravis

    • A skeletal muscle autoimmune disorder associated with loss of nAChRs at the neuromuscular junction
    • Symptoms include muscle weakness and fatigue, particularly affecting the muscles of the face and eyes
    • Diagnosed through blood testing for antibodies against nAChRs, edrophonium test, and single-fiber electromyography

    Myasthenia Gravis - Pharmacotherapy

    • Neostigmine: reversible competitive antagonist of AChE with a medium duration of action (1-2 hours)
    • Pyridostigmine: reversible competitive antagonist of AChE with a longer duration of action (30 minutes - 5 hours)
    • Edrophonium: reversible competitive antagonist of AChE with a short duration of action (10 minutes) used to diagnose myasthenia gravis
    • Corticosteroids: immunosuppressants that inhibit the genes coding for cytokines and TNFγ

    Congenital Myasthenic Syndrome (CMS)

    • Caused by mutations affecting nACh receptor expression, kinetics, agonist binding, or channel gating
    • Can be presynaptic (reduced ACh) or postsynaptic (reduced AChRs, fast channel CMS, slow channel CMS)
    • Mutations can affect presynaptic ACh vesicular transport, acetylcholinesterase activity, and expression of postsynaptic nicotinic acetylcholine receptors

    Neurosteroids and GABAA Receptor

    • Neurosteroids can directly activate GABAA receptors at high enough concentrations and under certain conditions
    • Allosteric binding of neurosteroids to the GABAA receptor increases the duration the ion channel remains open
    • Neurosteroid levels in the brain change during pregnancy, stress, and aging
    • Neurosteroid levels are altered by alcohol and some SSRI antidepressants
    • Postnatal depression, premenstrual tension, and certain epilepsies may be due to alterations in pregnane steroid levels in the brain

    Phasic and Tonic Conductance

    • Phasic conductance is mediated by postsynaptic receptors activated by synaptic GABA release
    • Tonic conductance is mediated by activation of extrasynaptic receptors by ambient concentrations of GABA.

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    Cys Loop Receptors PDF

    Description

    Explore the details of Cys-loop receptors, focusing on their pentameric protein structures and the role of nicotinic acetylcholine receptors in fast synaptic excitation. Understand how Myasthenia Gravis affects these receptors and leads to muscle weakness. Test your knowledge on their pharmacology and underlying mechanisms.

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