GABA B Receptor Function and Action Quiz

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Questions and Answers

What role does GABA B2 play in relation to GABA B1?

Increases GABA B1's agonist affinity. (correct)

Facilitates neurotransmitter release.

Directly binds to GABA.

Inhibits GABA B1 activation.

Which mechanism primarily inhibits neurotransmitter release under GABA B receptor activation?

Inhibition of adenylyl cyclase. (correct)

Reduction of G protein coupling.

Stimulation of cAMP levels.

Activation of voltage-dependent calcium channels.

Which G protein subunit is responsible for inhibiting voltage-dependent calcium channels?

Gα subunit

Gβγ subunit (correct)

G12/13 subunit

Gγ subunit

What effect do GABA B receptors have on cAMP levels when activated?

Reduce cAMP levels. Signup and view all the answers

What is the primary consequence of Gβγ subunits inhibiting the SNARE complex proteins?

Inhibition of neurotransmitter release. Signup and view all the answers

Which of the following correctly describes the GABA B receptor's mechanism of action?

It couples to Gi/o proteins to inhibit neurotransmitter release. Signup and view all the answers

What triggers exocytotic events during neurotransmitter release?

Binding of calcium to Synaptotagmin. Signup and view all the answers

Which statement best describes the interaction between GABA B2 and GABA?

GABA B2 does not bind GABA. Signup and view all the answers

What is the main effect of agonist binding on GPCRs?

It stabilizes the active conformation. Signup and view all the answers

What type of antagonist blocks GPCR activation by binding exclusively to the inactive state?

Negative antagonist Signup and view all the answers

Which mechanism illustrates the specificity of G protein coupling in GPCRs?

Transduction of active conformational changes to G proteins. Signup and view all the answers

Which type of GPCR is primarily known for its role in neurotransmitter signaling?

Dopamine receptors Signup and view all the answers

What is a characteristic feature of GPCR activation?

Conformational changes that activate G proteins. Signup and view all the answers

Which action is associated with GPCR desensitization?

Receptor internalization. Signup and view all the answers

In the context of GPCRs, what role do G proteins typically play?

They translate conformational changes into cellular responses. Signup and view all the answers

What effect does binding of a neutral antagonist have on GPCR activity?

It prevents transition into the active state. Signup and view all the answers

Which GPCR type is primarily involved in the modulation of acetylcholine signaling?

mAChRs Signup and view all the answers

How do ligand-induced conformational changes in GPCRs affect their functionality?

They enhance interactions between the receptor and G proteins. Signup and view all the answers

What is the primary structure involved in GPCR activation?

Transmembrane helices Signup and view all the answers

Which mechanism is involved in homologous desensitization of GPCRs?

Phosphorylation by specific kinases Signup and view all the answers

What is the role of β-arrestin in GPCR desensitization?

Facilitates receptor internalization Signup and view all the answers

Which type of GPCR is primarily associated with dopamine signaling?

Dopamine receptors Signup and view all the answers

What occurs during heterologous desensitization of GPCRs?

Receptor undergoes phosphorylation without ligand Signup and view all the answers

What effect does GRK-mediated phosphorylation have on GPCR activity?

Enables β-arrestin binding Signup and view all the answers

Which of the following GPCR types is specifically involved in muscarinic signal transduction?

mAChRs Signup and view all the answers

What is the consequence of G protein uncoupling in GPCR signaling?

Loss of cellular response to the ligand Signup and view all the answers

Study Notes

GABAB Receptor Subunit Function

GABA B2 subunit does not bind GABA
GABA B2 subunit interacts with GABA B1 subunit to stabilize its agonist-bound conformation
- This interaction increases agonist affinity
GABA B2 subunit is responsible for G protein coupling

GABAB Receptor Action

Activation of Gi/o protein leads to presynaptic inhibition of neurotransmitter release
Gα subunits inhibit adenylyl cyclase to reduce cAMP levels
Gβγ subunits inhibit
- Voltage-dependent Ca2+ channels
- SNARE complex proteins, preventing release

General Mechanisms of GPCR Modulation of Synaptic Transmission

Presynaptic GPCRs modulate neurotransmitter release
Inhibition of voltage-dependent calcium channels (VDCCs)
- Presynaptic membrane depolarization activates VDCCs
- Calcium influx binds to synaptotagmin to trigger exocytosis
- Gβγ-mediated inhibition of VDCCs decreases neurotransmitter release

Ligand-induced GPCR Conformational Changes

Agonist binding stabilizes the active conformation, shifting equilibrium toward the active state
Antagonist binding blocks activation
- Binding to the inactive state impedes transition to the active state (negative antagonism)
- Binding to both active and inactive conformations stabilizes the ratio and prevents a further transition into the active state (neutral antagonism)

G Protein Coupling

Ligand-induced conformational changes in GPCRs are transduced to the area of i3
- This is essential for G-protein coupling and activation

GPCR Desensitization

Heterologous desensitization does not require ligand binding
- PKA and PKC phosphorylate sites on the third intracellular loop and C-terminal cytoplasmic domain
- This phosphorylation inhibits binding to Gs
Homologous desensitization requires ligand binding
- G-protein receptor kinase (GRK)-mediated phosphorylation enables β-arrestin binding
- β-arrestin binding prevents Gs coupling
β-arrestin binding enhances the rate of GPCR internalization
GPCR ligand binding leads to homologous desensitization through two mechanisms
- Short-term desensitization through phosphorylation by GPCR kinases (GRKs), interaction with β-arrestin, and uncoupling of the interaction between the GPCR and the G protein
- Long-term desensitization through internalization, β-arrestin-mediated removal of the GPCR from the membrane, and degradation

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Description

Test your knowledge on the functions and actions of the GABA B receptor subunits. This quiz covers interactions between GABA B1 and GABA B2, the role of G proteins in neurotransmission, and the modulation of synaptic transmission by GPCRs. Dive deep into the mechanisms of presynaptic inhibition and ligand-induced receptor changes!