Intro to pharmacodynamics (lecture 1-3)

common radioisotopes

tritium (H3), iodine-125, halogen

orphan receptors

a receptor for which a ligand is unknown

receptor

a protein component of the cell which the drug binds to and leads to an effect on the cell

nonspecific binding site

a biological component a drug may bind to but is irrelevant

binding assay

lab method used to measure drug binding to R

components of drug binding assay

1. source of receptor

2. radiolabelled drug (hot) and unlabelled drug

3. buffer

how to calculate specific binding after performing a drug binding assay

Specific binding= total binding- nonspecific binding

how to measure total biding

1. Mix tissue (equal amounts), hot drug (inc. amounts), buffer

2. Incubate to equilibrium

3. Rapidly filter tissue and wash

to remove unbound drug

7. Count filters in a scintillation counter

How to measure nonspecific binding

1. Set up a second set of tubes

Add the same amount of tissue to each

Add increasing amounts of Hot drug

Add the same amount of Cold drug to all

tubes, but the concentration of Cold drug

Is 100 or 1000 times more than Hot drug.

2. Incubate to equilibrium

3. Filter samples and count as before

Remember the counter only counts the

Radioactive drug.

Bmax

maximum binding site and thus the tot

Specific activity (SA)

the amount of radioactivity per unit drug (Ci/mmol)

Binding Plot

concentration of drug required for 50% of receptor occupancy

Scatchard Plot

linear line

kd=-1/slope

Bmax= x intercept

competition binding curve

generated in an experiment where a fixed amount of a labeled molecule (the "hot" ligand) binds to a receptor, and its binding is reduced by increasing concentrations of an unlabeled molecule (the "cold" ligand) that competes for the same binding site

IC50

concentration of cold competitor at which binding of the radioligand is inhibited by 50% (a way to tell affinity)

Ki

Constant of inhibition calculated (assuming conc of kd is used) is ic50/2

Agonist

drug that bind and activate receptor

Antagonist

drugs that bind but do not activate receptors (neither on nor off)

Inverse agonist

drug that binds to receptor and induce the inactive state

basal state

no ligand, most receptors are in the inactive state

Activated state

with ligand active state is stabilized

agonist effect

alpha*conc DR

when ED50=Kd

direct effect

when EC50>Kd

multiple receptors must be occupied before the effect begins

when EC50<Kd

the effect becomes saturated before all receptors are occupied. in this case the system is said to have spare receptors

spare receptors

when each receptor activates an effector, a limited number of effectors even if there are more receptors

efficacy

defined by Emax, a maximum response

Potency

defined by EC50, an effect at a low concentration. a higher potent drug means a lower EC50

Propanolol

Competitive reversible antagonis

Competitive Reversible Antagonist

right shift EC50, and it does NOT effect Emax

ex. propanolol

Phenoxybenzamine

competitive irreversible antagonist

competitive irreversible antagonist

EC50 right shift, reduction of Emax

ex. phenoybenzamine

specificity vs selectivity

specificity→ molecule recognizees ONE specific compound

Selectivity → molecule preferentially recognize a compound

How many types of mAchR?

5 types ranging from M1-M5