## Receptor Types and Prevalence **Key Point:** G-protein coupled receptors (GPCRs) account for approximately 30–40% of all drug targets and are the most frequently exploited receptor class in clinical pharmacology. ### Classification of Receptor Mechanisms | Receptor Type | Mechanism | Prevalence | Clinical Examples | |---|---|---|---| | G-protein coupled receptors | Heterotrimeric G-protein activation | ~30–40% of drugs | β-blockers, ACE inhibitors, dopamine agonists | | Ligand-gated ion channels | Direct ion channel opening | ~5–10% of drugs | Benzodiazepines, succinylcholine | | Tyrosine kinase receptors | Autophosphorylation & cascade | ~5–10% of drugs | Trastuzumab, erlotinib | | Nuclear receptors | Gene transcription regulation | ~13% of drugs | Corticosteroids, thyroid hormone | ### Why GPCRs Dominate 1. **Structural diversity** — GPCRs comprise the largest protein family (>800 members in humans) 2. **Versatile signalling** — activate multiple downstream pathways (G~s~, G~i~, G~q~, G~12~) 3. **Tissue distribution** — expressed on virtually all cell types 4. **Druggability** — small molecules easily cross cell membranes to access the receptor **High-Yield:** Approximately **30–40%** of FDA-approved drugs target GPCRs. This is the single most exploited receptor class in therapeutics. **Clinical Pearl:** Common GPCR-targeting drugs include: - Cardiovascular: β-blockers (propranolol), α~2~-agonists (clonidine) - CNS: dopamine agonists (bromocriptine), serotonin antagonists (ondansetron) - Endocrine: GnRH agonists (leuprolide) ### Why Other Receptors Are Less Common - **Ligand-gated ion channels** — limited tissue distribution, slower onset, mainly for acute CNS/neuromuscular effects - **Tyrosine kinase receptors** — mostly growth factor signalling; fewer endogenous ligands; mainly targeted in oncology - **Nuclear receptors** — slower onset (gene transcription); limited to lipophilic drugs; ~13% of drug targets
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