## Most Common Receptor Type in Pharmacology **Key Point:** G-protein coupled receptors (GPCRs) represent the largest and most commonly targeted family of receptors in clinical pharmacology, accounting for approximately 30–40% of all FDA-approved drug targets. ### Distribution and Clinical Significance GPCRs are: - Present on virtually all cell types - Involved in regulation of neurotransmission, hormone signaling, sensory perception, and immune responses - The target of ~35% of all marketed drugs (e.g., β-blockers, muscarinic antagonists, dopamine agonists, serotonin antagonists) ### Comparison of Receptor Types | Receptor Type | Examples | Prevalence | Speed of Response | |---|---|---|---| | **G-protein coupled receptors** | β-adrenergic, muscarinic, dopamine, serotonin | Most common (~800 subtypes in humans) | Seconds to minutes | | Ligand-gated ion channels | Nicotinic, GABA~A~, NMDA | Moderate (~15 subtypes) | Milliseconds | | Tyrosine kinase receptors | EGF, PDGF, insulin receptors | Moderate (~58 subtypes) | Minutes | | Nuclear receptors | Steroid, thyroid, retinoic acid | Least common (~48 subtypes) | Hours | **High-Yield:** The term "G-protein coupled" refers to the intracellular coupling to heterotrimeric GTP-binding proteins (Gα, Gβ, Gγ), which transduce the signal via second messengers (cAMP, IP₃, DAG, Ca²⁺). **Clinical Pearl:** Most sympathomimetic, parasympathomimetic, and psychotropic drugs work through GPCRs, making this the most clinically relevant receptor family for NEET PG. **Mnemonic:** **GPCR = G-protein Coupled Receptor** — Remember "7-TM" (seven transmembrane domains) and "GTP activation" as the hallmark mechanism.
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