L5-8 Receptor Theory Flashcards
1
Q
What is the major target of drugs
A
Proteins
2
Q
What is a target of a select group of drugs, what type of drugs target this
A
DNA
Chemotherapy drugs
3
Q
Define a receptor
A
Proteins whose function it is to recognise and respond to endogenous chemical signals
4
Q
What are some examples of protein targets of drugs
A
Receptors
Enzymes
Transporters and Carriers
Ion channels
5
Q
Define a drug target
A
Other macro molecules which drugs interact with in order to produce their effects
6
Q
Receptors are classified by
A
Strucuture, pharmacology and signalling
7
Q
Receptors show _______ in the classes of drugs which they recognise
A
Specificity
8
Q
Are drugs 100% efficient
A
No, no drug is 100% specific
9
Q
What arises as a result of a loss of receptors
A
Disease
10
Q
Location of ligand gated ion channels
A
Membrane
11
Q
How many tm domains in ligand gated ion channels
A
Variable
12
Q
Where is the c’ term in ligand gated ion channels
A
Extracellular
13
Q
Where is the n’ term in ligand gated ion channels
A
EC
14
Q
What is the effector for a ligand gated ion channels
A
Ion channel
15
Q
What type of coupling involved in ligand gated ion channels
A
Direct
16
Q
Structure of ligand gated ion channels
A
Oligomeric assembly of subunits around a central pore
17
Q
Location of GPCRs
A
Membrane
18
Q
How many TM domains in GPCRs
A
7
19
Q
Where is the c’ term in GPCRs
A
IC
20
Q
What is the effector for GPCRs
A
Channel or enzyme
21
Q
Where is the n’ term for GPCRS
A
EC
22
Q
Coupling GPCRs
A
Via a G-protein
23
Q
Structure of a GPCR
A
Mon/oligomeric assemblt of 7 TM helicies with an IC G-protein coupling domain
24
Q
Location of kinase-linked receptors
A
Membrane
25
How many TM domaiins kinase-linked receptors
1
26
Where is c' term kinase-linked receptors
IC (catalytic domain)
27
Where is the n' term. kinase-linked receptors
EC (binding ligand domain)
28
Effector for kinase-linked receptors
Protein kinases
29
Coupling in kinase-linked receptors
Direct
30
Structure of kinase-linked receptors
Single Tm domain linked to EC receptor domain and IC catlytic domain
31
Location of nuclear receptors
Cytosol
32
Effector for nuclear receptors
Gene transcription via the DNA
33
Structure of a nuclear receptor
Monomeric structure with separate receptor and DNA binding domain
34
As downstream pathway
With GTP bound
Activation of adenylyl cyclases
Prod of cAMP
Act of PK-A
35
Ai downstream pathway
Inhibition of adenylyl cyclase
36
Aq downstream pathway
Act of PLC-B
| Breakdown of PIP(4,5)2 to IP3 and DAG
37
Occupation is governed by
Affinity
38
Activation is governed by
Efficacy
39
What does high specifity mean for the binding of drug to receptor
Binding will be strong
40
What does high specifity mean for the rate of the forward and reverse reaction
Rate forward will be high
| Rate backward will be low
41
A full agonist will have an efficacy of
E>0
42
An antagonist will have an antagonist of
E=0
43
Define occupancy
How many receptors are occupied by the drug and are forming the drug receptor comple
44
Occupancy will vary with
Drug concentration
45
Formula for occupancy
No receptors occupied / Total no. receptors
46
What scale is occupancy measure on
0 -1
0 no drug
1 fully occupied
47
Why is response NOT a good measure of occupancy
Response will vary with efficacy
48
Is occupancy directly proportional to occupancy
NO proportional - but not a 1:1 realationship
49
Define efficacy
The ability of the active form of the drug receptor complex to induce further downstream signalling
50
What is the method used to measure occupancy
A radioligand bidning assay
51
Method for accounting for non-specific binding in a radioligand binding assay
Two experiments in parrallel
In one - excess of cold ligand to displace the hot ligand from the specific bidning sites.
So any flourescence seen will be non specific binding (infinite number of binding sites)
So then specific binding = total bound - non specific binding
52
Conditions for purity in a radioligand binding assay
100% pure
| Free from chirality (optical isomerism)
53
Methods to prevent degredation in a radioligand binding assay
Free radical scavenger
Store at low temps
Avoid light
Incorporation of an anti-oxidant
54
Example of a free radical scavenger
Ethanol
55
Example of an anti-oxidant
Ascorbic acid
56
Characteristics of a good lable in a radioligand binding assay
High specifity
Low concentration of tracer (safe)
Does not impact on normal fucntion
57
3H is
Tritium
58
Advantages of using tritium as a radiolable
Radioactive form is indistinguishable from the natural form
High specific activities
Good stability
Long half life (~67 years)
59
Disadvantages of using tritium as a radiolabel
Hard to get homogenus group (i.e. getting the sam number of Hs labelled on each compound)
Specialist labs are required
Labelling is expensive and difficult
60
Advantages of using 125 I
If aromatic hydroxyl group (tyrosine residues in peptides) can be incorporated at high specific activities
Easy to use in labs
Cheap
61
Disadvantages of 125 I
More readily degraded
Biological activity of the ligand can be reduced
Short half-life (~67 years)
62
Characteritics of the tissue selected
Selected to contain the recog sites
Can be isolated membrane or whole organ
Dependent on the receptor and hypothesis
63
Incubation conditions for a radioligand binding assay
Preserve the integrity of the ligand and receptor
High enough protein content for assay volume
Additives added for protection
Temp close to 0
64
Why must temp be close to 0 during incubation
When cells homogenated, lysosomes ruptured, lysozyme enzyme released which would breakdown proteins
At a low temperature activity is low enough to protect the proteins
65
Two techniques usually used for spearation of bound from free
Filtration or centrifugation
66
What soluble binding techniques may be used to separate bound from free
Dialysis
Column chromatography
Precipitation/adsorption
67
The time available to separate depends on what
The KD
68
A low KD means
High affinity
69
A high KD means
Low affinity
70
If KD is low will you have long to separate
Yes
71
If the KD is high will you have long to separate
No
72
How to calculate specific binding from total bound and non specific
Specific = total - non specific
73
What is the shape o the total bound curve
Rectangular hyperbola
74
Why is specific binding saturable
Only a certain number of binding sites, eventually these will be full
75
How many non specific binding sites
Infinite
76
What is Bmax
The maximum occupancy
77
What is Kd
The disociation constant - concentration required for 50% occupancy
78
What is the equation linked to occupancy
Langmuir equation
79
Kd is a measure of
Affinity
80
Kd =
(k-1)/(k+1)
81
Lower KD means a
Higher affinity
82
Give the equation for bound drug at X concentration
(Bmax X Xa) // (Xa + Kd)
83
Give the equation for b/f from a scatchard plot
(Bmax - B) // Kd OR
B/F = 1/KD . (B-Bmax)
84
What does B represent
Bound radioligand
85
What does F represent
Free radioligand
86
What is the free radioligand equvilant to?
The ammount of drug added, concentration change due to some binding will be neglidgeable
87
What is Kd
The dissociation constant, concentration at which there is 100% occupancy
88
Bmax
Maximum ammount of drug which can specifically bind if one drug molecules binds to each receptor
89
Low Kd means
High affinity
90
High Kd mean
Low affinity
91
On a scatchard plot what is given by the slope of the graph
-1/KD
92
On a scatchard plot what is given by the x intercept
A ratio of B/F of zero => no bound
93
What is known if Kd is different
Must be a different receptor
94
Kd can be used to ___________ the ___________ of receptors
Quantify number
95
What disease involves a loss of receptors
Myasthenia gravis
96
What would be used to measure efficacy
A bioassay
97
Define EC50
Drug concentration which gives half of the maximum response capable of a tissue
98
Describe how Kd and EC50 values differ, why>
EC50 lower than Kd ==> 50% of the response is seen which less than 50% occupancy of the receptors
Due to receptor reserve or spare receptors
99
Why is there a receptor reserve
Signal amplification --> 1 activated receptor causes activation of many second messengers
MAX response may have been achieved - i.e. a muscle will only be able to contract to a certain degree
100
What is the hill equation used to determine
Response of a tissue to an agonist
101
What is the hill equation
(MAX . [Xa]^n) // ([Xa] + [EC50]^n)
102
What is MAX
Max response of a tissue
103
Xa =
Concentration of agonist
104
What is n
The slope factor -
| Determined by how many molecules of agonist need to bind to a receptor in order to activate it
105
What would the n number of a muscarinic receptor be
1
106
What would the n number of a nicotinic receptor be
2
107
EC50 is a measure of a drugs
Potency
108
What are the three things that potency depends on
Affinity, efficacy and the receptor reserve
109
What does a lower EC50 indicate
A greater potency
110
What does a higher EC50 indicate
A lower potency - more receptors need to be activated to induce 50% of the MAX response
111
What can be said about agonists A B and C in respect to their maximum responses and their EC50 value
Different maximum responses
| Same EC50 values
112
What is efficacy a measure of
A single agonist-receptor complexes ability to cause a response
113
What can be said about the occupancy for a partial agonist to elicit it's maximum response
All of the receptors have to be occupied
114
What are the three properties that determine the effect of a drug
Specificty
Affinity
Efficacy
115
Define specificity
The ability of a drug to interact with a structurally defined site/receptor
116
Define affinity
The ability of a drug to bind to a receptor
117
Define efficacy
The ability of a drug to cause activation of a receptor
118
What is the efficacy of a full agonist
E = 1
119
What is the efficacy of an antagonist
E = 0
120
What is an inverse agonist
A drug that when it binds to the receptor stabilises the resting state of that receptor reducing any constitutive activity
121
What is constitutive activity of a receptor
Where no agonist is bound but the receptor becomes spontaneously active
122
Define antagonist
A drug which prevents the response of an agonist - there are many types
123
Describe chemical antagonism
Substances which can combine in solution to chemically alter the agonist so that the active drug is lost
124
Example of a chemical antagonist
Heavy metal poisoning treating with chelating agents
125
What is a pharmacokinetic antagonist
Drug that causes a change in rate of metabolism, rate of absoprtion or rate of excretion
126
How do opiates act as pharmacokinetic antagonists
Affect GI tract motility, will reduce the effectiveness of any drugs which are taken by the oral route
127
What is warfarin used to treat, how does it show pharmacokinetic antagoism and why is this dangerous
```
Blood thinner (anti-coagulant) - taken in order to prevent heart attacks
Care must be taken when treated with some a.biotics as stimulate the metabolism of warafin and all of the effects are lost
```
128
What is physiological antagonism
Two drugs which act on different receptors to cause opposing effects within the body
129
How is arterial BP affected by physiological antagonism
NA --> Increases arterial BP
| Histamine --> Causes vasodilation thus lowering arterial BP
130
What is a non competitive antagonist
Substances which cause a block between receptor activation and response so no response is seen
131
How do dihydropyridines show non competitive antagonism
By blocking voltage gated calcium channels, preventing smooth muscle contraction
132
Define competitive antagonism
Directly compete with the agonist for occupancy of the receptor
133
What are the two types of competitive antagonists
Reversible and irreversible
134
What would happen to the dose response curve if reversible antagonist added, what about if more agonist was added ontop of this
Curve would shift (translate) right
135
What would happen to the max response and EC50 values if reversible antagonist added, what about if more agonist was added ontop of this
Max response would remain the same but ammount of agonist required would increase
EC50 would also increase
136
FOR COMP REVERSIBLE ANTAG
If concentration of agonists is ______ sufficiently the ______________________ increases and the effect of the antagonist ___________. This type of antagonism is _____________
Increased
Probability of an agonist binding specifically
Decreases
Surmountable
137
Define dose ratio
How many more times agonist is needed in the presence of an antagonist for the same response to be seen
138
Equation of dose ratio (DR)
[Agonist in presence of antagonist] // [Agonist without the antagonist]
139
A shild analysis is used to measure
Antagonist affinity
140
In a schild analysis what is DR given by
DR = (Xb/Kd) + 1
141
What is Xb
Concnetration of antagonist
142
What is Kd
Antagonist affinity contastnt
143
Whar is the equation of the line in a schild analysis
log(DR-1) = Log[Xb] - Log(Kd)
144
In a shild analysis what is plotted on the y axis
Log(DR-1)
145
In a schild analysis what is plotted on the x axis
Log(Xb)
146
The x intercept of a schild analysis is
- log(Kd)
147
Define Pa2
The negative log of molar concentration od the antagonist which will reduce the effect of double dose of the agonist drug to that of a single dose or -1*logKd
148
What can be said when DR
Double ammount of the receptor agonist is required for the same response to be seen
149
Pa2 =
logKd
150
What can be said about a higher Pa2 value
Higher the affintiy of the antagonist
151
If Pa2 is 9 what is KD
10^-9
152
Can irreversible competivie antagonism be reversed by washing
No
153
irreversible competivie antagonism is
Time dependent
154
Give an example of irreversible competitive antagonism
The effects of the alkylating drug bidenamine on histamine receptors in the guinea pig ileum
155
What condition cause desensitisation
When a drug is given continuously or repeatedly over a period of time
156
Desensitiation occurs due to
Loss of receptors from the cell surface
Change in the receptor - e.g. due to phosphorylation
Exhaustion of mediators
Increased metabolic degredation or extrusion of the drug
Physiological adapation
