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RECEPTOR PHARMACOLOGY
GENERAL ASPECTS OF RECEPTOR PHARMACOLOGY
STRUCTURAL AND FUNCTIONAL ASPECTS OF RECEPTORS
BY
Mahender.K
M.Pharm 1st yr 2nd sem.
Srikrupa institute of pharmaceutical sciences,
Velkatta,kondapak,medak.
Andhra pradesh.
Under the guidance of
Dr. T.Shivaraj gouda M.pharm.,PhD
H.O.D. (Pharmacology)

RECEPTOR
 A receptor is a molecule most often found on the
surface of a cell, which receives chemical signals
originating externally from the cell.
 Through binding to a receptor, these signals direct
a cell to do something—for example to divide or
die, or to allow certain molecules to enter or exit.

 Receptors are protein molecules, embedded in either the
plasma membrane (cell surface receptors) or the
cytoplasm or nucleus (nuclear receptors) of a cell, to
which one or more specific kinds of signaling molecules
may attach.
 A molecule which binds (attaches) to a receptor is called
a ligand, and may be a peptide (short protein) or other
small molecule, such as a neurotransmitter, a hormone, a
pharmaceutical drug, or a toxin.

 Numerous receptor types are found within a typical cell
and each type is linked to a specific biochemical
pathway.
 Furthermore each type of receptor recognizes and binds
only certain ligand shapes (in analogy to a lock and key
where the lock represents the receptor and the key, its
ligand).
 Hence the selective binding of specific a ligand to its
receptor activates or inhibits a specific biochemical
pathway.

CLASSIFICATION:
 By Modality and adequate stimulus
 Mechanical input - mechanoreceptors (touch, pressure, stretching, movements)
 Electromagnetic - photoreceptors (light)
 Chemoreceptors (taste, smell, oxygen level)
 Thermoreceptors (cold, warmth)
 Electrical – electroreceptors
 By Overall function
 Exteroreceptors - cutaneously located, responsible for providing information from the
immediate environment
 Telereceptors - sense events that originate at some distance from the body (such as in
eyes, ears, olfactory receptors)
 Interoceptors - respond to stimuli originating in the visceral organs
 Proprioceptors - convey information about the relative position of the body parts
(located in skeletal muscles, tendons, joints, vestibular apparatus)
 Clinical classification
 This classification is derived from the pathway by which the primary afferent axons
enter the CNS.
 Special sensory receptors - served by cranial nerves
 Cutaneous receptors - innervated by superficial branches of spinal and cranial nerves
 Deep receptors - located in muscles, tendons and joints, served by deeper branches of
spinal and cranial nerves
 Visceral receptors. - served by afferent axons associated with the autonomic nervous
system

LIGAND-GATED ION CHANNELS
 Ligand-gated ion channels (LGICs) are one type of ionotropic
receptor or channel-linked receptor. They are a group of
transmembrane ion channels that are opened or closed in response
to the binding of a chemical messenger (i.e., a ligand),such as a
neurotransmitter.
 The binding site of endogenous ligands on LGICs protein complexes
are normally located on a different portion of the protein (an allosteric
binding site) compared to where the ion conduction pore is located.
 The direct link between ligand binding and opening or closing of the
ion channel, which is characteristic of ligand-gated ion channels, is
contrasted with the indirect function of metabotropic receptors, which
use second messengers. LGICs are also different from voltage-gated
ion channels (which open and close depending on membrane
potential), and stretch-activated ion channels (which open and close
depending on mechanical deformation of the cell membrane)

 The five receptor sub units (2α,β,γ,δ) form a cluster
surrounding a central transmembrane pore, the
lining is formed by M2 hellical segment of each
subunit.
 These contains a preponderance of negatively
charged amino acids , which makes the pore cation
selective.
 There are two Ach binding sites in the extracellular
portion of the receptor, at the interface between the
alpha and the adjoining sub units.
 When two Ach binds the α helices swing out of the
way thus opening the channel pore.

G PROTEIN-COUPLED RECEPTOR
 It consists of a single polypeptide chain of up to
1100 residues.
 Their characteristic structure consists of 7 trans
membrane alpha helicessimilar to those of ion
channels, with an extracellular N terminal domain of
varying length and intracellular C terminal domain.

 It consists of three sub units which are anchored to the
membrane through attached lipase residues.
 Coupling of the alpha sub unit to an agonist occupied
receptor causes the bound GDP to exchange with
intracellular GTP the alpha GTP complex then
dissociates from the receptor and from the beta gamma
complex and interacts with a target protein(target 1),
which may also activate a target protein(target 2) .
 The GTPase activity of the alpha sub unit is increased
when the target protein is bound,leading to hydrolysis of
the bound GTP to GDP where upon the alpha sub unit
reunites with beta gamma.

KINASE LINKED RECPTORS
 These mediate the action of wide variety of protein
mediators including growth factors, cytokines and
hormones such as insulin and leptin whose effects
are exercted mainly at the level of gene
transcription.
 These are large proteins consisting of single chain
up to 1000 residues with a single membrane
spannig helical region assosiated with a large
extracellular ligand binding domain and intracellular
kinase domain.

 Receptors of various growth factors incorporate tyrosine
kinase in their intracellular domain.
 Cytokine receptors have an intracellular domain that
binds and activates cytosolic kinase when the receptor is
occupied.
 Signal transduction generally involves dimerisation of
receptors, followed by autophosporylation of tyrosine
residues. The posphotyrosine residues acts as acceptors
for SH2domains of intra cellular proteins,there by
allowing control of many cell functions,

NUCLEAR RECEPTORS
 Two main categories
o those that are present in the cytoplasm form homodimers
in the presence of their partner, and migrate to the
nucleus. Their ligands are endocrine in nature
(eg:steroidal hormones).
o those that are generally present in the nucleus and
form heterodimers with the retenoid X receptor. Their
ligands are usually lipids.(eg:fatty acids)
o third sub group tranduce mainly endocrine signals but
function as heterodimers with retenoid X receptor
.(eg:thyroid hormone)
 The receptor family is responsible for the pharmacology
of appx.10% and pharmacokinetics of 60% of all
prescribed drugs.

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