Neurotransmitter Receptors I: Ionotropic Receptors
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Questions and Answers

What is the first step in the life cycle of neurotransmission?

  • Storage
  • Transmitter Inactivation
  • Receptor Binding
  • Synthesis (correct)

Which of the following ionotropic receptor families is NOT mentioned in the outline?

  • GABA B receptor (correct)
  • Purinergic Receptors
  • nACh receptor
  • 5-HT3 Receptor

Which receptors are classified as glutamatergic ionotropic receptors?

  • AMPA/Kainate and NMDA receptors (correct)
  • 5-HT3 and Glycine receptors
  • nACh and GABAA receptors
  • Purinergic and GABAB receptors

During which stage of neurotransmission do neurotransmitters act on their respective receptors?

<p>Receptor Binding (C)</p> Signup and view all the answers

What role is indicated by transmitter inactivation in the life cycle of neurotransmission?

<p>Preventing excessive stimulation (B)</p> Signup and view all the answers

What structural feature of the M2 segment contributes to cation selectivity?

<p>Three rings of negatively charged amino acids toward the central pore (C)</p> Signup and view all the answers

How many molecules of ACh can each subunit of the nACh receptor bind?

<p>Five (C)</p> Signup and view all the answers

Where are the ACh binding sites located in the nACh receptor?

<p>At the interface between neighboring subunits (B)</p> Signup and view all the answers

What occurs when the ACh binding sites are occupied?

<p>The receptor opens to allow ion flow (D)</p> Signup and view all the answers

What indicates the transition from a closed to an open state in the nACh receptor?

<p>A subtle rotation of its M2 segments (C)</p> Signup and view all the answers

What is the composition of some neuronal nicotinic ACh receptors?

<p>Five identical subunits (D)</p> Signup and view all the answers

How does ACh gain access to its binding sites?

<p>By entering the central pore of the receptor (B)</p> Signup and view all the answers

What type of receptor is the nACh receptor classified as?

<p>Ionotropic receptor (D)</p> Signup and view all the answers

What is the primary function of GluN1 subunits in the NMDAR structure?

<p>They facilitate ion flow through the receptor pore. (D)</p> Signup and view all the answers

Which statement about NMDAR subunit composition is true?

<p>NMDARs can include a mix of GluN2 and GluN3 subunits. (D)</p> Signup and view all the answers

How can the contributions of NMDA and AMPA receptors to EPSC be differentiated?

<p>By applying pharmacological antagonists during voltage-clamp. (A)</p> Signup and view all the answers

What role do GluN2 subunits play within the NMDAR?

<p>They are responsible for the glutamate binding sites. (C)</p> Signup and view all the answers

What is a potential consequence of disrupted NMDAR function?

<p>Reduced synaptic transmission efficacy. (C)</p> Signup and view all the answers

What occurs in the presence of APV during an experiment to isolate NMDAR contributions?

<p>The current remaining represents AMPAR contributions. (D)</p> Signup and view all the answers

Which subunits directly provide the glycine-binding site in NMDARs?

<p>A combination of GluN1 or GluN3 subunits. (C)</p> Signup and view all the answers

What specific aspect of NMDA receptor functionality can be assessed through examining subunit diversity?

<p>The receptor properties and functionality. (A)</p> Signup and view all the answers

Which amino acid in GluA2 contributes to its low permeability to Ca2+?

<p>Arginine (D)</p> Signup and view all the answers

What impact does RNA editing have on GluA2's Ca2+ permeability?

<p>Decreases permeability (C)</p> Signup and view all the answers

What happens to GluA2 mRNA when the editing site complementary sequence (ECS) is deleted?

<p>Increases unedited GluA2 mRNA to approximately 25% (C)</p> Signup and view all the answers

What is the consequence of prolonged exposure to glutamate on AMPA receptors?

<p>Causes closure of the channel (D)</p> Signup and view all the answers

What is the likely effect of strong electrostatic repulsion in AMPA receptors?

<p>Reduced calcium permeability (C)</p> Signup and view all the answers

What kind of receptor is affected by RNA editing at the Q/R site?

<p>AMPA receptors (B)</p> Signup and view all the answers

Which process is disrupted when the editing site complementary sequence is impaired?

<p>GluA2 RNA editing (B)</p> Signup and view all the answers

What does the editing of the GluA2 amino acid primarily affect?

<p>The Ca2+ permeability of AMPA receptor channels (C)</p> Signup and view all the answers

Which of the following receptor types is characterized by being ionotropic and includes NMDA and non-NMDA subclasses?

<p>Glutamate receptors (D)</p> Signup and view all the answers

What mechanism causes ATP binding to influence the structure of purinergic receptors?

<p>Iris-like expansion of the pore region (C)</p> Signup and view all the answers

How many subunits come together to form the native receptor structure in purinergic receptors?

<p>Three (B)</p> Signup and view all the answers

Which pharmacological agents are mentioned as NMDA receptor antagonists?

<p>CNQX and APV (D)</p> Signup and view all the answers

In regards to glutamate receptors, what distinguishes the AMPA receptor from NMDA receptors?

<p>Calcium permeability (D)</p> Signup and view all the answers

What is the role of the M2 loop in AMPA receptors?

<p>Dips into and out of the cytoplasmic side (C)</p> Signup and view all the answers

Which characteristic of ionotropic receptors distinguishes them from metabotropic receptors?

<p>Directly mediating ion flow (B)</p> Signup and view all the answers

Which cation is NOT permeable through purinergic receptors?

<p>Mg2+ (B)</p> Signup and view all the answers

How many transmembrane domains does each subunit of a purinergic receptor contribute?

<p>Two (D)</p> Signup and view all the answers

Which receptor's agonists are under investigation for pharmacological distinction between subtypes?

<p>Glutamate receptors (B)</p> Signup and view all the answers

What can the binding of glutamate to AMPA receptors result in?

<p>Opening of ion channels for cation permeation (B)</p> Signup and view all the answers

What aspect of AMPA/Kainate receptors is essential for their assembly?

<p>Receptor trafficking processes (D)</p> Signup and view all the answers

What effect does phosphorylation have on the nACh receptor?

<p>Limits ion flux through transitions into a closed state (C)</p> Signup and view all the answers

Which subunits are phosphorylated by PKA in the nACh receptor?

<p>γ and δ subunits (D)</p> Signup and view all the answers

How are functional neuronal nACh receptors generally assembled?

<p>From multiple types of α and β subunits (C)</p> Signup and view all the answers

Which ion is specifically excluded from permeation through the 5-HT3 receptor?

<p>Ca2+ (D)</p> Signup and view all the answers

What is a common structural feature of GABAA receptors?

<p>Two α, two β, and one γ or δ subunit (C)</p> Signup and view all the answers

What is the primary role of antagonists for the 5-HT3 receptor?

<p>To treat vomiting and anxiety (D)</p> Signup and view all the answers

Which factor contributes to the tight ring blocking ion flow in the nACh receptor?

<p>Mild kink in the M2 segments (D)</p> Signup and view all the answers

What defines the desensitization rate of different nACh receptor types?

<p>The types of α and β subunits involved (D)</p> Signup and view all the answers

Which kinases phosphorylate the β subunit of the nACh receptor?

<p>Only an unidentified tyrosine kinase (A)</p> Signup and view all the answers

What structural feature is unique to neuronal nAChRs like α7 subtypes?

<p>Able to be assembled from a single subunit (B)</p> Signup and view all the answers

What primarily causes the flow of ions through the nACh receptor when bound with ACh?

<p>Conformational changes in the receptor structure (C)</p> Signup and view all the answers

What type of receptor family does the GABAA receptor belong to?

<p>Ionotropic receptors (C)</p> Signup and view all the answers

Which component is not included in the phosphorylation process of the nACh receptor?

<p>M1 segment (C)</p> Signup and view all the answers

What characterizes the assembly of distinct nACh receptor types?

<p>Flexibility in subunit combinations resulting in distinct functionalities (D)</p> Signup and view all the answers

Flashcards

NMDA Receptor Structure

NMDA receptors (NMDARs) are composed of two GluN1 subunits and either two GluN2 subunits or a combination of GluN2 and GluN3 subunits.

GluN1 Subunit Function

GluN1 is crucial for creating the receptor's ion channel pore, enabling ion flow.

GluN1/3 Subunit Function

GluN1 and GluN3 subunits provide the glycine-binding site for the NMDA receptor.

GluN2 Subunit Function

GluN2 subunits contain the glutamate binding sites for the NMDA receptor.

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Subunit Composition Effect

The specific combination of NMDA receptor subunits, influences the receptor's properties.

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NMDA Receptor Function

NMDA receptors contribute to excitatory postsynaptic currents (EPSCs), the electrical signals in synapses.

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AMPAR Contribution

AMPA receptors, when studied alongside NMDA receptors in a voltage-clamp, contribute to the measurable postsynaptic current.

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NMDARs Contribution

The difference between the total EPSC trace and the trace after APV application is the contribution of NMDA receptors.

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Ionotropic Receptors

Neurotransmitter receptors that directly open ion channels upon binding to neurotransmitters.

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Neurotransmitter Release Outcome

Neurotransmitter release leads to specific changes in the postsynaptic neuron, often generating electrical signals.

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Neurotransmitter Inactivation

Methods used to terminate the signal of a neurotransmitter after it binds to its receptor.

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5-HT3 Receptor Family

A class of ionotropic receptors that respond to serotonin (5-hydroxytryptamine).

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nACh Receptors

Ionotropic receptors that respond to acetylcholine.

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M2 segment arrangement

Amino acids in the M2 segment form three rings of negative charges facing the channel's center.

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Cation selectivity

The channel's negative charge rings attract positive ions (cations).

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nACh Receptor subunits

Some nicotinic acetylcholine receptors have five identical subunits.

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ACh binding sites location

Acetylcholine binding sites are at subunit interfaces.

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ACh access to binding sites

ACh enters the receptor's central pore to reach the binding sites.

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Receptor opening

Binding triggers rapid opening in the ion channel.

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M2 segment rotation

The change from closed to open state involves a small shift in the M2 segments.

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nAChR function

The receptor opens to allow ion flow, crucial for signal transmission.

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AMPA Receptor Ca2+ Permeability

AMPA receptors with GluA2 have very low calcium permeability due to electrostatic repulsion.

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RNA Editing in GluA2

RNA editing in GluA2 changes a single amino acid, reducing calcium permeability.

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GluA2 RNA Editing Site Deletion

Deleting the editing site (ECS) in the intron reduces GluA2 RNA editing, leading to less editing.

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AMPA Receptor Desensitization

Extended glutamate exposure changes the dimer bond, closing the channel.

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Glutamate Exposure Effect

Extended exposure to glutamate causes AMPA receptor desensitization, changing the shape of the protein and closing the channel

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Ca2+ Permeability

The ability of a channel to allow calcium ions to pass through.

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RNA Editing

A process that modifies the RNA sequence.

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ECS(Explanatory Complement Sequence) impact on GluA2

Removing the ECS impairs GluA2 Q/R site editing, leading to less Q/R changed mRNA.

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Purinergic Receptors

These receptors respond to ATP, a key signaling molecule.

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Ionotropic Receptors

Neurotransmitter receptors that directly open ion channels upon binding to neurotransmitters.

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Receptor Subunit Assembly

Multiple subunits combine to form functional receptors

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Glutamatergic Receptors

These receptors respond to glutamate, a key excitatory neurotransmitter.

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AMPA/Kainate Receptors

Types of ionotropic glutamate receptors that are key for fast synaptic transmission

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NMDA Receptors

Glutamate receptors with specialized properties that play a role in learning and memory.

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Non-NMDA Receptors

Sub-category for ionotropic glutamate receptors without specific NMDA properties.

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AMPA Receptor Structure

These receptors are made of multiple parts, including transmembrane helices and a loop that influences their function.

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Transmembrane Domains (TM)

Protein segments that span the cell membrane.

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Receptor Assembly and Trafficking

The process by which receptor subunits come together and move to their correct locations in the cell.

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ATP Binding

The process in which ATP binds to its receptors

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Ion Channel Pore Region Expansion

Process where the pore opens in response to a signaling molecule

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Transmembrane Helix Twisting

A change in the structure of transmembrane helices due to ligand binding

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Ca2+ Permeation

Movement of calcium ions through channels

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Cation Permeation

Movement of positively charged ions through ion channels

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nACh Receptor Structure

nACh receptors have M2 segments that form a kinked ring, blocking ion flow.

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nACh Receptor Activation

Acetylcholine (ACh) binding causes M2 segments to rotate, relaxing the constriction, and allowing ion flow.

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nACh Receptor Subunits

nAChRs can be assembled from different subunit combinations, creating diverse receptor types.

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nACh Receptor Kinases

PKA, PKC and unidentified tyrosine kinases phosphorylate nAChR subunits influencing desensitization.

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nAChR Phosphorylation

Phosphorylation affects the receptor's speed of desensitization(rapid closure).

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5-HT3 Receptor Subunits

5-HT3 receptors are a group of receptors built from five identical subunits.

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5-HT3 Receptor Ion Permeability

5-HT3 receptors primarily allow sodium and potassium ions to pass through, not calcium.

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5-HT3 Receptor Location

5-HT3 receptors are found in nerve endings and the central nervous system.

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GABAA Receptor Composition

GABAA receptors typically have two alpha, two beta, and one gamma or delta subunit.

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nACh Receptor Types

nACh receptors can form from a single subunit, like in alpha7, alpha8, or alpha9 or from multiple subunits e.g alpha3/beta2 or alpha3/beta4.

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Ionotropic Receptors

Ionotropic receptors are directly coupled to ion channels; opening ion channels when bound by neurotransmitters

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Ion flow through channels

A flow of ions through a channel can affect the membrane potential of the cell.

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Ion channel opening

Ligand binding triggers a conformational change, opening the channel.

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nAChR Desensitization

Phosphorylation increases desensitization; limiting the activity of the response.

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Study Notes

Neurotransmitter Receptors I: Ionotropic Receptors

  • Ionotropic receptors are a type of neurotransmitter receptor
  • These receptors directly gate ion channels
  • Neurotransmission involves a cycle of events
  • Synthesis, Storage, Release, Receptor Binding, and Transmission inactivation are key stages

The Life Cycle of Neurotransmission

  • I. Synthesis (1-2): Neurotransmitters are produced
  • II. Storage (3): Neurotransmitters are stored in vesicles
  • III. Release (Lecture 4): Neurotransmitters are released into the synaptic cleft
  • IV. Receptor Binding (4-5): Neurotransmitters bind to receptors on the postsynaptic membrane.
  • V. Transmitter Inactivation (6-9): Neurotransmitters are removed from the synaptic cleft

Lecture Outline

  • Overview of ionotropic receptor families
  • nACh receptor, 5-HT3 receptor, GABA-A and Glycine Receptors, Purinergic Receptors, Glutamatergic Ionotropic Receptors, AMPA/Kainate, NMDA, Receptor Localization
  • Outcome of neurotransmitter release: Type of response - postsynaptic receptor, Magnitude of response - receptor number, "state" of the receptors, and amount of neurotransmitter released

Lonotropic and Metabotropic Receptors

  • Direct gating vs indirect gating
  • Fast actions last only milliseconds, while slower actions last seconds to minutes

nACh Receptor: an Iconic lonotropic Receptor

  • Receptor made up of subunits
  • Two extracellular binding sites for Ach
  • Plant alkaloid nicotine activates the receptor
  • Ion flow occurs through the channel

nACh Receptor: an Iconic lonotropic Receptor

  • Each subunit provides a component to form an ion channel
  • Hydrophobic regions (M1-M4) form α-helices spanning the membrane.
  • Negatively charged amino acids contribute to cation selectivity in the channel pore.

5-HT3 Receptor

  • Homomeric complex (five copies of the same subunit)
  • Permeable to Na+ and K+, but not Ca2+
  • Located on peripheral primary sensory nerve endings and the mammalian CNS

GABA, and Glycine Receptors

  • GABA receptors are typically composed of two α, two β, and one γ or δ subunit.
  • GABA binding activates the channel, allowing chloride ion influx.
  • Glycine receptors are composed of three α and two β subunits, and require multiple glycine molecules for activation.

GABA Receptors and Disease

  • Repetitive seizures result from a decrease in GABAAR β3 subunit phosphorylation by PKC.
  • This leads to increased internalization of synaptic GABA receptors.
  • This causes a reduced inhibitory effect.

Purinergic Receptors

  • lonotropic receptors for ATP (adenosine triphosphate)
  • ATP serves as an excitatory transmitter.

Glutamate Receptors

  • Development of agonists that can pharmacologically distinguish between different glutamate receptor subtypes
  • N-methyl-D-aspartate (NMDA), α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), Kainate

AMPA Receptors

  • Receptor assembly and trafficking
  • Three transmembrane α-helices (M1, M3, and M4) and a loop (M2)
  • The M2 loop forms the selectivity filter in the channel
  • Glutamate binding activates the channel, enabling sodium and potassium ion flow
  • RNA editing of GluA2 can alter the calcium permeability of the channel

NMDA Receptors

  • Critical role in development, learning, and memory, and brain injury
  • Permeable to calcium, glycine, and voltage-dependent
  • Important in controlling neuronal excitability
  • Membrane depolarization expels Mg²⁺ to allow ion flow.

TARPs: Stargazin

  • Stargazin increases AMPAR expression at the synapse by increasing the number of AMPA receptors in the membrane.
  • Stargazin modulates AMPA receptor trafficking, affecting their localization and function.
  • Affects glutamate receptor function and synaptic plasticity.

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Neurotransmitter Receptors I: Ionotropic Receptors PDF

Description

This quiz covers the key concepts of ionotropic receptors, a type of neurotransmitter receptor that directly gates ion channels. It includes an overview of the neurotransmission life cycle, including synthesis, storage, release, receptor binding, and inactivation. Learn about specific ionotropic receptor families such as nACh, GABA-A, and NMDA receptors.

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