Enlist the different type of receptors with examples of drugs acting through them
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drug receptors pharmacology
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types of drug receptors ligand gated ion channels G protein coupled enzyme linked intracellular receptor pharmacology
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The main pharmacological classification has four receptor types:
| Receptor type | Basic mechanism | Examples of receptors | Examples of drugs acting through them |
|---|---|---|---|
| 1. Ligand-gated ion channel receptors | Ligand binding directly opens or closes an ion channel. Very rapid action, usually milliseconds. | Nicotinic ACh, GABA-A, NMDA, 5-HT3 receptors | Nicotine and suxamethonium: nicotinic ACh receptor agonists; benzodiazepines: enhance GABA-A receptor action; ondansetron: 5-HT3 receptor antagonist; ketamine: NMDA receptor antagonist |
| 2. G-protein-coupled receptors (GPCRs) | Seven-transmembrane receptors coupled to G proteins and second messengers such as cAMP, IP3/DAG, and Ca²⁺. Action in seconds to minutes. | Adrenergic, muscarinic, opioid, dopamine, histamine, serotonin receptors except 5-HT3 | Salbutamol: β2-adrenergic agonist; propranolol: β-adrenergic antagonist; atropine: muscarinic antagonist; morphine: μ-opioid agonist; cetirizine: H1 antagonist |
| 3. Enzyme-linked or kinase-linked receptors | Receptor has intrinsic enzyme activity or is coupled to intracellular enzymes, commonly tyrosine kinase or JAK-STAT pathways. Action in minutes to hours. | Insulin receptor, epidermal growth factor receptor, cytokine receptors for erythropoietin and growth hormone, atrial natriuretic peptide receptor | Insulin: insulin receptor with intrinsic tyrosine-kinase activity; erythropoietin: JAK-STAT-linked cytokine receptor; somatropin: growth-hormone receptor, JAK-STAT; nesiritide: natriuretic-peptide receptor with guanylyl cyclase activity |
| 4. Intracellular or nuclear receptors | Lipid-soluble drug enters the cell, binds cytoplasmic/nuclear receptor, and alters gene transcription. Slow onset, hours to days. | Glucocorticoid, mineralocorticoid, estrogen, progesterone, androgen, thyroid-hormone, vitamin-D receptors | Prednisolone/dexamethasone: glucocorticoid receptor agonists; levothyroxine: thyroid-hormone receptor agonist; calcitriol: vitamin-D receptor agonist; tamoxifen: selective estrogen-receptor modulator |
Easy mnemonic: I-G-E-N
- Ion channel-linked
- G-protein-coupled
- Enzyme-linked
- Nuclear/intracellular
Nicotinic ACh receptors are ligand-gated ion channels, whereas muscarinic ACh receptors are GPCRs. This illustrates how the same endogenous transmitter can act through different receptor classes. The standard membrane-receptor grouping into channel-linked, GPCR, and enzyme-linked receptors, with intracellular receptors for membrane-permeant ligands, is described by NCBI Neuroscience. Katzung notes that steroids, thyroid hormone, and vitamin D act through intracellular receptors that regulate transcription, while nicotinic ACh receptors are ligand-gated ion channels.
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