Receptors I Flashcards
What drug type creates a response in the cell
agonist
What is occupation of a drug-receptor governed by?
Affinity
What is activation of a drug-receptor governed by?
efficacy
What part of a drug receptor reaction is reversible
occupation forming a complex
What is the ratio of reversibility of a drug receptor reaction governed by?
affinity of the drug
Describe the reversibility of drugs with high affinities
slow reversibility
Describe occupancy
proportion of receptors occupied will vary with the drug concentration
What does occupancy vary between
0 and 1
How much drug is present at 0 occupancy
none
How can we measure occupancy
by measuring response
Describe the relationship between occupancy and response
high occupancy means there is a large response
Can you measure antagonists activity using occupancy
NO
Examples of ligands
neurotransmitters, hormones, growth factors, cytokines, drugs, toxins
Examples of protein targets
receptors, ion channels, enzymes, transporters
Describe a ligand binding practical
tissue prep with radio-ligand, incubation, filtration, rinse, count, data analysis
True or False - most ligands bind non-specifically to tissue, filter paper, glass
TRUE
How can non-specific ligand binding be reduced
reduced by anti-absorbants
What are some examples of anti-absorbants
albumin, collagen, o-catechol
What is the function of rinsing in a ligand binding practical
remove unbound radioligand from incubation medium
What is a key measurement in receptor ligand assays
specific and non specific binding
What are the disadvantages of using a radio ligand
degradation
How can you prevent degradation of radio ligands
free radical scavenger, store at low temp, avoid light, incorporation of antioxidant
What are radio ligands labelled with
radio active labels
Name two radio labels
tritum, iodine
What are the disadvantages of tritum
specialised labs required, expensive
What are the advantages of tritum as a label
high specific activities, good stability, long half life
What are the advantages of iodine as a label
easy and cheap, if aromatic hydroxyl group can be incorporated at high specific activities
What are the disadvantages of iodine
more readily degraded, short half life, activity of ligand can be reduced
What tissue would you select for your ligand binding practical
tissue that contains the receptors of interest
What can the tissue be in the ligand binding practical
isolated membranes, slices, synaptosomes, purified receptors
What must incubation preserve
integrity of ligands and binding sites
What happens during the tissue incubation period of the ligand binding practical
enzymes are liberated
What is the effect of enzymes being liberated during the tissue incubation period
enzymes break down receptors of interest
What are the enzymes liberated during the tissue incubation period
proteases
How can the effect of enzymes be minimised during the tissue incubation period
protease inhibitors added for peptides, anti-oxidants if ligand is oxidisable
What is the temperature during the incubation period
low room temperature to 0 degrees
How is the tissue and bound ligand separated from free ligand
filtration or centrifugation
What is a problem when separating bound ligand from free ligand during the practical
rate of dissociation of ligand-receptor complex
What must speed of separation of bound ligand from free ligand be compatible with
affinity of ligand for receptor
What type of separation does lower affinity of ligand receptor require
faster/more efficient separation
How do you work out specific binding
subtract non specific binding from total bound
How is ligand receptor binding data plotted
semi-logarithmic scale
What is saturable binding
specific binding
Why is radio-ligand binding saturable
total number of receptors is limited
What does the Langmuir equation describe
relationship between receptor occupancy, affinity and drug concentration
What is Bmax in the Scatchard equation
maximum amount of drug which can bind specifically to receptors
What is F in the Scatchard equation
free ligand concentration
What is KD in the scatchard equation
dissociation constant for radio ligand
What determines the dissociation constant for the radio ligand
saturation analysis
What is KD a measure of
affinity
What does high KD show
low affinity
