Q5. Which adrenergic or muscarinic receptor subtype is coupled to the Gs protein?

Appeared in: INI-CET EXAM -2026

Explanation

Beta adrenergic receptors are classic examples of receptors coupled to the Gs (stimulatory) protein.
Activation of Beta receptors by agonists like epinephrine or norepinephrine leads to the activation of the Gs protein.
The activated Gs protein stimulates the effector enzyme adenylyl cyclase.
Adenylyl cyclase catalyzes the conversion of ATP to the second messenger cyclic AMP (cAMP).
Elevated cAMP levels then activate Protein Kinase A (PKA), leading to phosphorylation of downstream targets and producing physiological effects like increased heart rate (β1) and bronchodilation (β2).

Option A: The M1 muscarinic receptor is not coupled to Gs. It is coupled to the Gq protein.
Option B: The M2 muscarinic receptor is coupled to the Gi (inhibitory) protein, not Gs.
Option C: This is a broad category. Alpha-1 adrenergic receptors are coupled to Gq, and Alpha-2 adrenergic receptors are coupled to Gi. Neither is coupled to Gs.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain G-Protein Coupled Receptor (GPCR) Signaling Pathways as background academic context rather than a clinical decision trigger.
Understanding receptor-G protein coupling is fundamental to pharmacology. Many drugs are designed to target these pathways.
For example, Beta-blockers (e.g., metoprolol) are antagonists at β1-receptors. They are used to treat hypertension and angina by blocking the Gs-mediated increase in heart rate and contractility.
Beta-2 agonists (e.g., albuterol) are used as bronchodilators in asthma. They activate the Gs pathway in bronchial smooth muscle, leading to increased cAMP and muscle relaxation.

How to Approach the Question

First, identify the core of the question: it asks to link a specific receptor type to the Gs protein.
Recall the main families of G-proteins: Gs (stimulatory), Gi (inhibitory), and Gq.
Systematically review the options and their known G-protein couplings.
Mnemonic for Adrenergic Receptors: A helpful mnemonic for adrenergic receptor coupling is 'QISS' (pronounced 'kiss'): α1 -> Gq; α2 -> Gi; β1 -> Gs; β2 -> Gs.
Recall that M1 and M3 muscarinic receptors are typically Gq-coupled, while M2 and M4 are Gi-coupled.
Based on this knowledge, identify that Beta adrenergic receptors are the ones coupled to Gs.

Concept Tested & Keywords

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E6 Pharmacology Katzung 16e pp. 215-217, 168-170, 55-57, 154-156

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