Receptors and Basic Pharm Flashcards
Drugs exert their effect by…..
binding to a receptor (protein)
Receptors act as a……..
signal transducer
when receptors bind a drug they send some sort of signal tot he cell machinery to produce a physiological effect
agonists
drugs that actively produce a physiological effect
antagonists
drugs that block the action of agonists
a binding curve of a drug bound to a receptor vs free drug concentration looks like…..
a rectangular hyberbola
having 100% of the receptor bound by drug is a limit approached as the drug concentrations gets….
very high
define the dissociation constant describing drug binding to its receptor
the concentration of drug providing 1/2 maximal binding
semilog plots (drug bound to receptor) vs log (free drug) provide….
sigmoidal curves that allow a more complete range of data to be shown.
Note: linear curves don’t allow such a large range of data to be plotted. Pharmacologists like to express data over a 1000 fold or more range of drug concentration. When plotted on a semilog plot the data goes from a rectangular hyperbola to a sigmoidal curve.
most drugs function by interacting with?
receptor proteins and either facilitating (agonist drugs) or blocking (antagonist drugs) their function
Pilocarpine……. salivation by the submaxillary gland and atropine…… this effect
stimulates salivation
blocks this effect
pilocarpine and atropine product their effects by acting upon…..
muscarinic acetylcholine receptor proteins of the salivary glands
muscarinic antagonists can produce…
xerostomia
Summarize Langley’s experiment (the origin of the cell receptor theory)
Drugs A and B can bind to a receptor Y. They compete based on how much of each drug is present and how well each can bind to the receptor.
Note: this is true for competitive antagonists
Langley concluded that cells have what 2 distinct things?
- ) chief substance- concerned with carrying out the chief functions of the cells (contraction, secretion, formation of metabolic products etc.)
- ) receptive substances- liable to change and capable of setting the chief substance into action
nicotine is an….
agonist
curare is an….
antagonist
interaction of a drug with a receptor is based on the law of…
mass action
describe the rate of association and dissociation relative to each other at equilibruim
they’re equal
k1 [Lf] [R]
rate of association
R- receptor
Lf- free drug
k-1 [RL]
rate of dissociation
Kd
dissociation constant
[R] [L] / [RL] = Kd
how to plot drug bound to receptor vs drug concentration
[RL] = ?
what is the shape of the graph?
[RL] = [Rt] [Lf] / (Kd + [Lf])
Rt- total receptors
Lf- free drug
rectangular hyperbola
As Lf approaches infinity RL/Rt approaches?
it approaches 1
aka. once the drug concentration is high enough, basically all of the receptor will contain bound drug
When RL / Rt = 1/2, Lf = ?
Lf = Kd
aka. the equilibrium dissociation constant (Kd) describes the drug concentration required for 1/2 maximal binding to occur
Is it possible that two drugs L1 and L2 act at the same receptor site but require vastly different concentration to achieve the same effect?
Yes.
Drug binding depends how much drug is available for binding (concentration) as well as the dissociation constant Kd. If drug L1 has a higher Kd than drug L2, more of drug L1 will be required to achieve equivalent binding to L2.
If X amount of drug produces a certain effect, will 2x the amount of drug produce roughly twice as much of an effect?
No, not necessarily. Probably not.
It depends on where you are on the binding curve. if the amount of drug bound to receptor is low, doubling the amount of drug will roughly double the amount of drug bound to the receptor which MAY double the effect. However if the amount of drug bound to the receptor is high, doubling the amount of drug will have little to no effect.
