Drug Receptors
Learn what drug receptors are, how drug-receptor interactions produce pharmacological effects, major receptor types, agonists, antagonists, selectivity, and clinical examples.
| Receptor Type | Location | Mechanism of Action | Primary Signaling Pathway | Onset of Action | Duration of Effect | Key Examples | Clinical Examples |
|---|---|---|---|---|---|---|---|
| Ligand-Gated Ion Channels | Cell membrane | Ligand binding directly opens or closes an ion channel, altering ion flow across the membrane | Na⁺, K⁺, Ca²⁺ or Cl⁻ movement | Very rapid — milliseconds | Short | Nicotinic ACh, GABAA, NMDA receptors | Benzodiazepines → GABAA; nicotine → nicotinic ACh receptors |
| G Protein-Coupled Receptors (GPCRs) | Cell membrane | Ligand activates G proteins that regulate enzymes or ion channels | cAMP, IP₃/DAG, Ca²⁺ and other second messengers | Seconds to minutes | Seconds to hours | β-adrenergic, muscarinic, opioid, dopamine receptors | Salbutamol → β₂; morphine → μ-opioid |
| Enzyme-Linked / Catalytic Receptors | Cell membrane | Ligand binding activates intrinsic enzymatic activity or an associated enzyme, often a protein kinase | Phosphorylation cascades such as PI3K-AKT and MAPK pathways | Minutes to hours | Hours or longer | Insulin receptor, epidermal growth factor receptor | Insulin → insulin receptor; growth factors → receptor tyrosine kinases |
| Intracellular / Nuclear Receptors | Cytoplasm and/or nucleus | Lipophilic ligand enters the cell and binds an intracellular receptor, altering gene transcription | Regulation of DNA transcription and protein synthesis | Slow — hours to days | Long-lasting | Glucocorticoid, estrogen, androgen, thyroid hormone receptors | Prednisolone → glucocorticoid receptor; estradiol → estrogen receptor |