Receptors are protein molecules located in cell membranes, cytosol, and nuclei that bind to ligands such as drugs. Ligand binding alters enzyme activity, ion permeability, and genetic material conformation. Receptors serve dual functions by recognizing specific ligands and initiating biochemical reactions that transmit signals from ligands to intracellular proteins. The interaction between ligands and receptors is characterized by selectivity, based on physico-chemical properties, and affinity, which measures the strength of binding. Agonists elicit pharmacological responses by binding with high affinity and intrinsic activity, while antagonists block receptors through high affinity but lack intrinsic activity. Partial agonists have lower intrinsic activity than full agonists. Inverse agonists produce effects opposite to agonists.

1. RECEPTOR & LIGANDS
PRESENTED BY
PHARMACOLOGY-I
HEENA PARVEEN
ASST.PROFESSOR .
MRCP.

2. RECEPTOR
Receptors are specific protein macromolecules in C.M, Cytosol,Nucleus.
Many drugs(ligands) bind to (i) Receptors for endogenous substances,
(ii) Enzymes,
(iii) Other constituents,which serves as
Receptors for drugs.
Ligand binding alters Enzyme activity,
Changes permeability to ions,
Confirmational changes in the genetic material
of nucleus..

3. LOCK & KEY MODEL

4. Receptor serves as a dual function:
It acts as recognition molecule for specific ligands
It initiates biochemical reactions which transmit the signal from
ligand to proteins in the cell membrane & within the cell.
Biologically a receptor is inactive till ligand binds to it, only then it gets
activated & triggers the post-receptor events .
Interaction between ligand & Receptor are characterized by principal
parametres: SELECTIVITY & AFFINITY

5. Affinity-A measure of the strength of binding b/w Drug & Receptor.
Selectivity- depends on the physico-chemical properties of drug & receptor.
Efficacy- Ability of a drug to elicit a response after its interaction with the
receptor is also termed as Intrinsic activity.
AGONIST- A drug which initiates pharmacological action after binding to the
recptors .A drug with HIGH AFFINITY & INTRINSIC ACTIVITY.
ANTAGONIST- A drug which also binds to the receptors but doesn’t elicit a
pharmacological action ,it causes Receptor blockade.
A drug with HIGH AFFINITY & POOR INTRINSIC ACTIVITY.

10. PARTIAL AGONIST
A drug with affinity equal to and less than that of agonist but less intrinsic activity.
This drug,no matter how high its conc, will not produce full response which the tissue is
capable of.

11. INVERSE AGONIST
After combination with a receptor ,a drug may produce actions opposite to those
produced by a pure agonist.

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