Definitions Flashcards
Antagonist
A drug that binds to a receptor and prevents activation
affinity but no efficacy
several diff types; competitive, non competitive and uncompetitive
Greater Emax =
Greater efficacy
Smaller EC50
higher potency
Bmax
The maximum binding obtained in a saturation assay
corresponds to the number of receptors in the system
rectangular hyperbola
a curve that rises and then smoothly reaches a plateau.
characteristic of concentration-binding relationships.
predicted by Hill-Langmuir equation
Ki
may mean 2 diff things
someties used to define the afffinity of a competitive antagonist
more often used to define the affinity of a ligand and derived from a concentration binding assay
Conc ratio
ratio of agonist EC50 in the presence of antagonist to the Ec50 in the absence. for a competitive antagonist but it is more often used to define the degree of ‘right shift’ on the agonist concentration response curve
Gaddum equation
An equation used to describe the actions of a competitive antagonist.
EC50
The conc. of an agonist that gives 50%of the max response
sigmoid curve
S shaped curve, seen with log conc. response relationships
Receptor
A protein involved in cell signalling.
takes a signal, binds it, passes on info that signal conveys.
important drug binding sites
Kd
equilibrium dissociation constant used to measure drug affinity
is the conc. of a ligand that occupies 50% of a receptor population and thus as Kd increases so affinity decreases
Full agonist
a drug that gives the max response possible from a receptor
Partial agonist
drug that activates a receptor, but not to the same degree as a full agonis.
It is ‘part way’ between a full agonist and an antagonist
Affinity
tightness with which a drug binds to a receptor or other protein. It is usually measured by the equilibrium dissociation constant, Kd. As Kd increases, affinity decreases
Agonist
A drug that binds to a receptor and activates it. It has both affinity and efficacy
Potency
conc. of drug required to produce a defined effect.
ec50 is often used as a measure of agonist potency
for antagonists, PA2 is the most frequently used parameter
PA2
Conc of competitive antagonist such that twice the concentration of agonist is required to restore the original response for a competitive antagonist, the PA2 is theoretically equal to -logKi
Emax
maximal effectthat can be obtained from a functional assay. It may depend on both receptor and system factors
ED50
dose that produces 50% of maximal response. This term should only be used when drug responses are measured in animals or mans
PKd
-ve log of Kd. A drug with a Kd of 1e^-9M has a pKd of 9
Hill Langmuir Equation
the basic equation relating the binding of a drug to its conc. It can be derived from the Laws of Mass Action
Non-competitive antagonist
An antagonist that binds to a receptor at a site other than the agonist binding site. The EC50 for agonist is unchanged but the max response is decreased.
unsurmountable by agonist conc
IC50
Conc of an agonist that reduces response to a particular conc. of agonist by 50%
Efficacy
the degree to which an agonist can activate a receptor. A full agonist has the maximal possible efficacy. An antagonist has zero efficacy. A partial agonist has some efficacy, but less than that of a full agonist
pEC50
negative log of the EC50
competitive antagonist
a drug that binds to the same site as an agonist, but does not activate the receptor. The presence of a competitive antagonist will reduce occupancy by agonists. In a functional assay, a competitive antagonist will cause a parallel rightward shift in the agonist conc response curve
Selectivity
the ability of a drug to bind more tightly (or activate more potently) one receptor type compared with another. A drug with an affinity of 1nM for receptor X and 10nM for receptor Y has 10 fold selectivity for receptor x
Drugs acting on adrenergic transmission
Cardiovascular system (diverse) Anti-asthma drugs Decongestants Aphrodisiacs Migraine ADHD Depression
