34 Questions
Which type of ligand-gated ion channel mediates membrane hyperpolarization?
GABAAR
How many subunits typically make up a Cys-loop receptor in the LGIC family?
Five
Which type of ion does GABAAR allow to flow through the open channel?
Chloride ions
Which of the following is a characteristic feature of Ionotropic Glutamate Receptors?
Non-selective cation channels
What is the typical subunit composition of the Muscle (NM) subtype of nAChR?
2α1, β1, δ, & γ/ε subunits
Which neurotransmitter activates the Nicotinic Acetylcholine Receptor (nAChR)?
Acetylcholine
Propofol is known to modulate which type of ligand-gated ion channel?
GABAAR
Neurosteroids are capable of influencing the activity of which type of receptor?
GABAAR
Ethanol is known to affect which type of ion flow through a ligand-gated channel?
Chloride ions
What is the main characteristic of ligand-gated ion channels (LGICs) mentioned in the text?
Incorporate extracellular ligand-binding sites
Which receptor type among the major receptor superfamily utilizes the G-protein-coupled pathway?
GABAA receptors
What is the primary function of GABAA receptors?
Inhibit neurotransmission
Which type of ligand binds to GABAA receptors to activate them?
GABA
How does the activation of GABAA receptors typically affect cellular function?
Inhibits neuronal activity
What type of ions flow into/out of the cell through the activated GABAA receptor channel?
Calcium and chloride ions
How do neurosteroids modulate GABAA receptors?
By enhancing GABAergic inhibition
How does propofol modulate GABAA receptors?
By enhancing receptor response to GABA
Why is it important to understand the subunit composition of GABAA receptors?
It influences the pharmacological properties of the receptor.
What distinguishes synaptic GABAA receptors from extrasynaptic ones?
Different cellular expression pattern.
Which type of GABAA receptors typically contain a δ-subunit and α4, α5, or α6 subunits?
Extrasynaptic receptors
Which subunits are generally formed from two α-subunits, two β-subunits, and either a γ- or δ-subunit in GABAA receptors?
α1 and β2 subunits
Which drug is preferentially modulated by extrasynaptic GABAA receptors?
Propofol
Where are synaptic GABAA receptors typically located?
Within the synaptic cleft
Which of the following is NOT a ligand-gated ion channel receptor?
Neuronal subtype receptor
What ions predominantly flow through GABAA receptor channels upon activation?
$Cl^-$ ions
Which subunit classes are cloned for GABAA receptors according to the text?
$eta$ and $ ho$ subunits
What is the key functional role of the NN subtype of GABAA receptors?
Modulation of transmitter release
Which drugs allosterically modulate GABAA receptors according to the text?
Benzodiazepines & Alcohol
What plays a key role as the main inhibitory transmitter in the brain according to the text?
GABA (Gamma-aminobutyric acid)
Describe the subclassification basis of ligand-gated ion channels.
The subclassification is based on the type of ligand that binds to the receptor.
What are the key characteristic features of the major ligand-gated ion channel families?
The key characteristic features include molecular structure, subtypes, cellular expression, and functional roles.
Describe the molecular structure, subtypes, cellular expression, and functional role of nicotinic acetylcholine receptors (nAChRs).
Nicotinic acetylcholine receptors are pentameric ligand-gated ion channels, expressed in the central and peripheral nervous systems, and play a role in excitatory neurotransmission.
Describe the molecular structure, subtypes, cellular expression, and functional role of GABAA receptors (GABAARs).
GABAA receptors are pentameric ligand-gated ion channels, expressed in the brain, and primarily function as inhibitory neurotransmitters.
What are the unique features/characteristics of the ligand-gated ion channel superfamily?
The ligand-gated ion channel superfamily consists of multimeric integral membrane proteins with extracellular ligand-binding sites and a central transmembrane ion-permeable channel/pore.
Study Notes
Ligand-Gated Ion Channels (LGICs)
- LGICs are a type of receptor that allows ions to flow into the cell when a ligand binds to it
- Classified into two main categories: excitatory (cation-selective) and inhibitory (anion-selective) ion channels
Excitatory LGICs
- Mediate influx of cations (e.g. Na+, Ca++) into the cell
- Cause membrane depolarization
- Examples: nAChR, 5-HT3R, ionotropic glutamate receptors (NMDA, AMPA, and kainate), and P2X receptors
Inhibitory LGICs
- Mediate influx of anions (e.g. Cl-) into the cell
- Cause membrane hyperpolarization
- Examples: GABAAR and glycine receptors
Cys-loop Receptor Family
- Characterized by a disulfide Cys-loop in the extracellular domain
- Examples: nAChR, 5-HT3R, GABAAR, and glycine receptors
- Subunits share a common structure with a large extracellular domain, 4 transmembrane α-helices, and a short extracellular C-terminal domain
Nicotinic Acetylcholine Receptor (nAChR)
- Activated endogenously by acetylcholine
- Also activated by nicotine
- Occurs in the central and peripheral nervous system
- Mediates fast synaptic transmission in the nervous system and at the somatic neuromuscular junction (NMJ)
- Plays key roles in controlling skeletal muscle contraction, and modulation of neuronal excitability and integration, gene expression, learning and memory formation, and neuroprotection
Molecular Structure and Function of nAChR
- Pentameric complexes composed of 5 subunits
- 17 nAChR subunits cloned: α1-α10, β1-β4, γ, δ, and ε
- Subunits co-assemble to form functional homo- or heteropentameric receptors
- Muscle (NM) subtype typically comprises 2α1, β1, δ, and γ/ε subunits
- Neuronal (NN) subtype typically comprises 2α and 3β subunits (hetero-pentamers) or 5α7 subunits (homo-pentamers)
GABAAR Receptor
- Activated endogenously by GABA
- Occurs widely in the CNS
- Mediates fast (phasic) and slow (tonic) neuronal inhibition
- Plays key roles in controlling feeding behavior, circadian rhythm, sleep-wake cycle, vigilance, learning, and memory
- Implicated in anxiety/sleep disorders, depression, mania, autism, psychosis, and alcoholism
Allosteric Modulation of GABAAR
- GABAARs have multiple ligand binding sites
- Allosteric modulators bind to specific binding sites on GABAARs and enhance or potentiate the effects of GABA
- Examples: benzodiazepines, barbiturates, neurosteroids, general anesthetics, and alcohol
Test your knowledge on neuronal subtypes and receptor superfamilies in the Central Nervous System. Explore key functional roles including modulation of transmitter release, gene expression, cognition, and neuroprotection. Focus on the role of Muscle Type nAChRs in skeletal muscle contraction.
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