pharmacology

Lecture #5
Pharmacodynamic
SIGNAL TRANSDUCTION
The drug–receptor complex
Receptor states
Receptors exist in at least two states, inactive (R) and active (R*),
that are in reversible equilibrium with one another, usually favoring the
inactive state. Binding of agonists causes the equilibrium to shift from
R to R* to produce a biologic effect. Antagonists occupy the receptor
but do not increase the fraction of R* and may stabilize the receptor in
the inactive state. Some drugs (partial agonists) cause similar shifts in
equilibrium from R to R*, but the fraction of R* is less than that caused
by an agonist (but still more than that caused by an antagonist). The
magnitude of biological effect is directly related to the fraction of R*.
Agonists, antagonists, and partial agonists are examples of ligands,
or molecules that bind to the activation site on the receptor.
.
Major receptor families

1. Transmembrane ligand-gated ion channels
2. Transmembrane G protein–coupled receptors
3. Enzyme-linked receptors
4. Intracellular receptors

Some characteristics of signal transduction
1. Signal amplification
2. Desensitization and down-regulation of receptors


A B C D