Receptor’ is any target molecule with which a drug molecule has to combine in order to elicit its specific effect

Receptor’ is any target molecule with which a drug molecule has to combine in order to elicit its specific effect.
For example, the voltage-sensitive sodium channel is sometimes referred to as the ‘receptor’ for local anaesthetics
Receptors largely determine the quantitative relations between dose or concentration of drug and pharmacologic effects.
Receptors are responsible for drug action.
Receptors mediate the actions of both pharmacologic agonists and antagonists
Type of drug-receptor interaction:
Agonist :Direct +Indirect ,Full ,Partial
Agonist:
The drug that produces ………response when it binds to the receptor.
(high efficacy)
Partial agonist:
The drug that produces ……..response when it binds to the receptor. (intermediate efficacy)
Antagonist:
Cell surface receptors exist to transmit chemical signals from the outside to the inside of the cell.Some compounds bind to cell surface receptors, yet do not activate the receptors to trigger a response.When cell surface receptors bind the molecule, the endogenous chemical cannot bind to the receptor and cannot trigger a response.The compound is said to “antagonize” or “block” the receptor and is referred to as a receptor antagonist.

Type 1: ligand-gated ion channels:
Also known as ionotropic receptors.
These are membrane proteins with a similar structure to other ion channels, and incorporate a ligand-binding (receptor) site, usually in the extracellular domain. Typically, these are the receptors on which fast neurotransmitters act.
Examples include the nicotinic acetylcholine receptor (nAChR; GABAA receptor; and glutamate receptors of the NMDA, and kainate types

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Type 2: G-protein-coupled receptors (GPCRs)
Known as metabotropic receptors or 7-transmembrane-spanning (heptahelical) receptors.
They are membrane receptors that are coupled to intracellular effector systems via a G-protein.
They constitute the largest family, and include receptors for many hormones and slow transmitters.
Examples: the muscarinic acetylcholine receptors and adrenergic receptors
Type 3: Tyrosine-kinase receptors
Structure:
Receptors exist as individual polypeptides
Each has an extracellular signal-binding site
An intracellular tail with a number of tyrosines and a single å helix spanning the membrane

Type 4: Intracellular receptors
Not all signal receptors are located on the plasma membrane. Some are proteins located in the cytoplasm or nucleus of target cells.
The signal molecule must be able to pass through plasma membrane.
Examples: Steroid (e.g., estradiol, progesterone, testosterone).

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