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Receptors / Dose Response Flashcards

1
Q

Ligands

A

Molecules bound by receptors

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2
Q

Agonist

A

Molecule that binds receptor —> produces biological response

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3
Q

Antagonist

A

Molecule that binds a receptor but does not induce a biological response (endogenous mediators blocked)

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4
Q

Characteristics of a receptor

A

Saturability
Specificity
Reversibility
Bifunctional role

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5
Q

Classes of receptors

A

Ion channel receptors
G-protein coupled receptors
Tyrosine kinase receptors
Transcription factor receptors

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6
Q

Examples of ion channel receptors

A

Neurotransmitter receptors (e.g., acetylcholine, GABA, Aspartate, glycine)

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7
Q

Characteristic of ion channel receptors

A

Very fast (millisecond)

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8
Q

Examples of G-protein coupled receptors

A

Neurotransmitters, peptide hormones, biogenic amines

40-50% of pharmaceutical targets are GPCRs

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9
Q

Characteristics of GPCRs

A

G-protein - transducing agent that couples active receptor to cellular response; binds GTP then uncouples from activated receptor

Fast 100s of ms to second

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10
Q

Receptor pathways

A

Receptor to activate and/or inhibit pathway

Receptor can act on / activate multiple pathways

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11
Q

Pathways of GPCRs

A

GPCRs can link to more than one G-protein

GPCRs may initiate cell signaling not traditionally associated with G-proteins

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12
Q

Examples of tyrosine kinase receptors

A

Receptor for insulin, growth factors

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13
Q

Characteristics of tyrosine kinase receptor

A

Slower action - order of minutes

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14
Q

Transcription factor receptors

A

Receptors for steroids, thyroid hormone, vit D, retinoids

Intracellular receptor —> agonists must be hydrophobic to pass through the membrane and bind

Very slow - hours to days

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15
Q

Rate of receptor classes

A

Ion channel > GPCR > tyrosine kinase > transcription factor

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16
Q

Receptor subtypes

A

May have differential distribution —> can exploit for tissue specificity

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17
Q

Receptor affinity

A

ratio of off rate of a ligand binding a receptor to on rate (dissociation constant, Kd)

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18
Q

High affinity

A

Very slow off rate

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19
Q

Lower affinity

A

Faster off rate

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20
Q

No affinity

A

No on rate

21
Q

Saturation isotherm

A

Directly measures binding of a radio labeled ligand to receptor

22
Q

Competition binding assay

A

Compares ability of nonradioactive ligands to compete with radioligand to bind to a receptor

23
Q

Measuring total binding

A
  1. combine tissue + radiolabeled drug
  2. Incubate
  3. Wash off unbound drug
  4. Measure radioactivity
24
Q

Total binding curve

A

Binding experiment done with the same amount of tissue in each tube but with INCREASING conc of radioligand

Aka saturation isotherm

25
Measuring non-specific binding
1. Combine tissue + radiolabeled drug + excess of non-radioactive competing ligand 2. Incubate 3. Wash off unbound drug 4. Measure radioactivity
26
Non-specific binding curve
Binding experiment the same as for the total binding curve, but in the presence of high does of competing non-radioactivity ligand Used to correct the total curve to get the specific binding curve
27
Plateau of the binding curve represents
Saturability
28
A lower Kd corresponds to a _____ receptor affinity
Higher
29
Kd
Concentration of ligand where half maximal binding is obtained
30
Competition binding analysis
Measure of % specific radioligand binding relative to increasing concentration of competitor
31
IC50 in competition binding analysis
Concentration of competitor which inhibits binding by 50%
32
Lower IC50 in competition binding analysis means …
The competitor has a higher receptor affinity
33
Dose response curves
Linear plot - hemiparabolic with plateau at saturation; proportional to receptors occupied Semi log plot - used to be able to display a wider range of doses; sigmoid shape
34
Dose-response curve of antagonist / non-binder
Flat line on semi log curve
35
Dose response curves of agonists
Sigmoid shape EC50 - concentration with half-maximal response Lower EC50 —> more potent agonist
36
Dose-response curve for partial agonist
Fails to reach full response (i.e. doesn’t reach saturation point of full agonist)
37
Intrinsic efficacy
Ability of ligands to activate receptors Full agonists - max response; intrinsic efficacy = 1 Partial agonist - less than maximal; 0 < intrinsic efficacy < 1 Antagonist - no response, intrinsic efficacy = 0
38
Molecular basis of intrinsic efficacy
Full agonist: full activation of receptor (i.e. binding + full interaction with activation domain) Partial agonist: partial activation of receptor (i.e. binding + partial interaction with activation domain) Antagonist: no response (i.e. binds receptor but not activation domain)
39
Potency of a ligand is determined by …
Fractional occupancy (binding) + Intrinsic efficacy (ability to activate)
40
Effect of competitive antagonist on dose response curve
Pretreatment with competitive antagonist directly blocks binding, but with high enough agonist concentration will be displaced Curve shifts to the right (need higher conc to reach saturation)
41
Effect of non competitive antagonist on dose-response curve
Non-competitive antagonist doesn’t block binding of agonist, but prevents subsequent activity upon binding With antagonist pre-treatment, will need a higher conc to illicit activity, but also will not reach maximum Dose response curve shifts right and downward
42
Inverse agonist
Binds and induces a biological response in the opposite direction of an agonist
43
Other factors impacting the biological response
Spare receptors - shift does response curve left (Greater response despite equivalent concentration of agonist - % receptors bound is the same, but the overall # bound is higher) Large threshold for response - shift curve right
44
Receptor desensitization
Receptor can still bind agonist, but cell signaling is disrupted
45
Receptor downregulation
Receptor pulled off cell surface
46
Drug tolerance develops in response to
Receptor desensitization Receptor downregulation Elongates/flattens out the slope of the dose response curve (down/right shift)
47
Drug vacation
When receptor desensitization / downregulation occur; switch to a medication that acts by a DIFFERENT pathway to allow original pathway to resensitize
48
Receptor supersensitivity
Response following denervation —> nerve dies —> upregulation of receptors that make tissue supersensitive to any neurotransmitter

Pharm (10 decks)

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