Test 1: lecture 7-8 Flashcards
what does agonist do?
binds and causes cellular response
what does antagonist cause?
binds to receptor and has NO effect
4 criteria for being receptor
- Saturability
- Specificity
- Reversibility- ligand can attach and detach
- Bifunctional Role
4 classes of receptors
example of ion channel receptor
many neurotransmitter receptors, e.g. acetylcholine (nicotinic), GABA, aspartate, glycine.
neurotransmitter binds: ion channels open, ions flow through down concentration gradiant (immediate)
how does ion channel receptor work
neurotransmitter binds: ion channels open, ions flow through down concentration gradiant (immediate)
very fast, milliseconds
examples of G-protein coupled receptors
neurotransmitters, most peptide hormones, some biogenic amines (e.g. catecholamines, serotonin).
Nearly 1000 genes in the human genome encodes for proteins in — class of receptors 40 - 50% of pharmaceuticals in the market today act on these receptors
G-protein coupled receptors
how does G-protein coupled receptor work
ligand binds
causes change in structure
GTP comes in and bumps off GDP
alpha(GTP) and gamma(beta) uncouple and cause down stream effects
fast,100s of ms to seconds
- Transducing agent that couples the activated receptor to the cellular response
- Trimeric protein
- Binds GTP and then uncouples from receptor upon receptor activation
AT1 receptors can —
have several intracellular responses (both + and -)
G-protein coupled receptors can link to more than one G-protein.
G-protein coupled receptors may be able to initiate cell signaling not traditionally associated with G-proteins.
how does tyrosine kinase receptor work?
ligand bins
dimerizes
autophosphorylation
cause chain reaction of adding phosphate to targets in cells
cause intracellular signals (seriers of kinases)
Receptors for insulin, growth factors (growth hormone)
examples of tyrosine kinase receptors
Receptors for insulin, growth factors (growth hormone)
how long does tyrosine kinase receptor take?
minutes
Receptors for insulin, growth factors (growth hormone)
what are some transcription factor receptors?
Receptors for steroids, thyroid hormone, vitamin D, retinoids
hydrophobic (can move through membrane)
how do transcription factor receptors work
ligand moves into cell, binds in cytoplasm, moves to nucleus, change genes made
Receptors for steroids, thyroid hormone, vitamin D, retinoids
very slow, hours to days
how fast are transcription factor receptors
very slow, hours to days
fastest to slowest receptor classes
many receptors systems have — which are distributed in the body in specific areas
subtypes
can make drug target specific receptor in specific tissue
Kd
dissociation constant= (Koff)/(Kon)
free/bound
how tightly ligand is bound to the receptor
two types of binding analyses
saturation isotherm
competition bind analysis
how to make saturation isotherm graph
tubes of same amount of tissue and increasing amount of radiolabeled drugs
washed through filter
count radioactibity associated with tissue on the filter: can have bound and unwashed unbound drug
this is a total binding curve which means Binding experiment done with — amount of tissue in each tube but with — concentrations of radioligand
same
increasing
how to measure nonspecific binding of radioligand binding?
combine tissue, radioligand and excessive amounts of nonradioactive competing ligand
filter
the competing ligand will bind to tissue, any radioactivity on the filter is from unbound drug stuck to filter (not important) can be used to subtract from total to get actual radioacivity of the sample→ specific
NON-SPECIFIC BINDING CURVE: Binding experiment is same as for Total Binding Curve but in the presence of high dose of — ligand
COMPETING NONRADIOACTIVE
how to get specific saturation isotherm curve
total- nonspecific
total: all radioactivity on filter, bound and free radioligand
nonspecific: noncompetive bound to tissue, all radioligand attached to filter
what is Bmax?
maximal number of binding site= y axis (top of curve)
what is KD?
concentration of radioligand where half maximal binding is obtained
x axis equal to 1/2 Bmax
lower KD = — receptor affinity
higher
Kd= (Koff/Kon)
Kd= concentration of radioligand where half maximal binding (1/2Bmax) is obatined
higher Kd = — receptor affinity
lower
high Kd means takes longer for ligand to bind to receptor
how does competition binding analysis curve created?
measure radioactivity of a drug
and then slowly increase competiting non radioactivity until there is only competing ligand attached to the receptors
Competition binding analysis measures the ability of the — ligand to compete off the radioligand in the binding to the same receptors.
NON-radioactive
what is IC50?
concentration of competitor which inhibits binding by 50%. rank order of potency should correspond with their biological potency
lower IC50= higher receptor affinity in comparing competitors
decreased radioactivity= more competiting ligand
pink curve has no affinity for receptor= does not kickoff radioactivty ligand
explain pink vs red
this graph is showing the same ligand and receptor with different competition ligands
pink competition ligand does not bind/ has no affinity for the receptor
orange: competition ligand binds to receptor
IC50 is where 50% of radioactive ligand has been kicked off receptor
lower IC50= higher receptor affinity in comparing competitors
dose response curve shows Effect of drug was thought to be proportional to the fraction of receptors occupied by the drug. Maximal effect when all receptors are —
occupied.
more drug= more recptors bound
has max effect when receptors are saturated
which curve is the antagonist?
red= flat
either antagonist= binds but nothing happens
or
drug does not bind at all
which curve has the lowest EC50?
what does that mean?
EC50= amount of drug needed to fill 50% of receptors (to create half max response)
lower EC50 means a more potent agonist
which drug has the lower Kd
Kd for black is lower then Kd for orange
lower EC50= more potent agonist
which curve is agonist, partial agonist, antagonist?
The ability of ligands to activate receptors is not an all or none property, but is actually a graded property.
intrinsic efficacy
FULL AGONISTS
* Get maximal response
* Intrinsic Efficacy = 1
PARTIAL AGONIST
* Less than maximal response
* Intrinsic Efficacy between 0 and 1
ANTAGONIST
* No response
* Intrinsic Efficacy = 0
what kind of receptor has intrinsic efficacy of 0
antagonist= no reponse
intrinsic efficacy= The ability of ligands to activate receptors is not an all or none property, but is actually a graded property.
what type of receptor has intrinsic efficacy of 1
full agonist
gets maximal response
intrinsic efficacy= The ability of ligands to activate receptors is not an all or none property, but is actually a graded property.
what type of receptor has intrinsic efficacy of 0-1
partial agonist
less than maximal response
intrinsic efficacy= The ability of ligands to activate receptors is not an all or none property, but is actually a graded property.
the effect/potency of a ligand is determined by — and —
fractional occupancy (how many receptors bound)
intrinisic efficacy (how well the ligand activates the receptor)
what happens to does response curve with competitive antagonist?
still gets to max, but needs more of original drug to get there
parallel shift of dose response curve to right without affecting maximal response
what is red curve?
non competitive antagonists
how does non competitive antagonist effect the dose response curve?
takes more drug, but never gets to max
- Antagonist causes reduced efficacy of agonist, maximum response no longer achieved.
- Covalent modification of receptor or interacting regulatory site is possible. May involve destruction of receptors
- Shift of dose-response curve to right WITH REDUCTION OF MAXIMAL RESPONSE.
An — induces a biological response upon binding to the receptor, BUT in OPPOSITE direction compared to an agonist.
inverse agonist
if normal agonist causes increased cAMP, then inverse agonist does the opposite → would cause decreased cAMP
what will spare receptors cause
hypersensitive reaction
would reach max, much faster then normal binding
Because of a surplus of receptors, can get a GREATER level of response despite an EQUIVALENT concentration of agonist
Because of a surplus of receptors, can get an EQUIVALENT level of response from a LOWER concentration of agonist
Because of a surplus of receptors, can get a GREATER level of response despite an — concentration of agonist
EQUIVALENT
Because of a surplus of receptors, can get an EQUIVALENT level of response from a — concentration of agonist
LOWER
decreased amount of drug would cause same reaction cause there are more receptors to start intercellular reaction
what is receptor desensitization
over time same amount of drug will have decreased effect
if you take away drug, give body time to recover, you can restart drug to get original response levels
what is receptor downregulation
cell will move receptor off of cell wall in response to long term drug
if you take away drug, receptors will move back to cell wall
can then give drug again
explain receptor supersensitivity after denervation
cell is used to getting drug from nerve
nerve damaged= no drug
cell tries to find drug by increasing amount of receptors on its wall
if nerve repaired and impulse comes back, there are now too many receptors and will cause very large response/supersensitive
