Essay on Pharmacodynamics (Drug Receptors)

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Dose of drug administered


Drug in tissues

Drug in systemic circulation

Drug metabolized or excreted

Drug at site of action

Pharmacologic effect Pharmacodynamics Toxicity Efficacy

PHARMACOLOGY Pharmacodynamics
Actions of drug on the body  Specific to a drug/ class of drugs • Interaction with target sites (receptors/enzymes) • Effects at site of action • Dose-response relationship • Reduction in symptoms • Modification of disease process • Unwanted/side effects • Drug interactions • Inter- and intra-patient differences

Actions of body on the drug  Non-specific, general processes • Absorption from site of administration • Distribution to the
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 Non-conducting

 Closed but openable in reponse

to appropriate stimulus

Activated (open) 3. Inactivated

 Closed and unable to open in

response to appropriate stimulus for rested state channel

When ligand binds to the ligand-binding site  Conformation change in other parts of ROC molecule  Opening of central, ion-selective pore  Increase transmembrane conductance  Alters electrical potential across the membrane  Transmits signal across plasma membrane

Acetylcholine binds to the nicotinic acetylcholine receptor
 Opening of ion channel  Allows Na+ to flow down its

concentration gradient into cells  Produce a localised excitatory postsynaptic potential (a depolarization)

Similar to ROC  But operated by voltage, instead of ligands  Examples:

Cardiac Na+ channel Ca2+ selective VOC K+ selective VOC

Cellular response occur in the range of milliseconds after binding of agonist to a ligand-gated channel

(4) G-Protein Coupled Receptor

Receptor located on cell membrane  G protein

› A complex of 3

subunits (α, β and γ) › A transduction component › Energy dependent (ATP, GDP)

In the rested state (When no ligand is present)
G protein o Subunits are bound together o GDP (Guanine nucleotide diphosphate) is tightly bound to the α subunit of the G protein

G protein in this