pharmacology

Question 1

how many TM domains do ligand gated ion channels have?

Answer 1

4 or 5

Question 2

what does protein kinase A do?

Answer 2

phosphorylate proteins on serine and threonine residues which have a hydroxyl group

Question 3

what does arrestin do?

Answer 3

binds to g-protein coupled receptors and arrests their function + stops signalling
involved in desensitisation

Question 4

describe the g protein signalling cascade

Answer 4

1. agonist binds to G-protein coupled receptor
2. receptor undergoes conformational change —> activates g protein
3. α subunit unbinds to β and γ subunit
4. α subunit bind GTP —> activates
5. α subunit activates downstream signalling pathway

Question 5

describe the signalling pathway activated by Gs α subunit

Answer 5

1. α subunit activates adenylyl cyclase
2. adenlyl cyclase converts ATP to cAMP
3. cAMP activates PKA

Question 6

describe the signalling pathway activated by the Gi α subunit

Answer 6

α subunit inhibits adenylyl cyclase

Question 7

describe the signalling pathway activated by the Gq α subunit

Answer 7

1. α subunit activates phospholipase Cβ

2. phospholipase Cβ breaks down PIP2 to produce IP3 and DAG

Question 8

what is the purpose of the βγ subunits in G proteins?

Answer 8

regulates gating of certain ion channels

Question 9

DEFINE: affinity

Answer 9

measure of how well the drug and ligand bind each other. fast forward reaction and slow backward reaction.

Question 10

DEFINE: occupancy

Answer 10

measure of how many receptors are occupied by drugs and forming drug-receptor complexes

Question 11

DEFINE: efficacy

Answer 11

the ability of a drug to produce a maximum response

Question 12

how would you reduce non-specific binding to filters and glass?

Answer 12

anti-absorbants
e.g. albumin or collagen for peptides
O-catechol for catecholamines

Question 13

radioligand binding assay

Answer 13

1. 1st set of tubes = tissue + radioactive ligand
   bound radioactivity = specific binding + non-specific binding
2. 2nd set of tubes = tissue + radioactive ligand + non-radioactive ligand
   non-radioactive ligand outcompetes radioactive ligand for specific binding sites. non specific binding not displaced.
   bound radioactivity = non-specific binding
3. specific binding = total bound - non-specific binding

Question 14

how to avoid degradation of ligand?

Answer 14

• free radical scavengers (e.g. ethanol) in drug solution
• storing in dark bottles to avoid light
• storing at low temps
• add antioxidant (e.g. ascorbic acid) to minimise oxidation

Question 15

what are the advantages and disadvantages of using 3H?

Answer 15

:) labelled product indistinguishable from native compound
:) stabile
:) long half-life
:) high specific activities can be obtained
:( specialised labs required
:( labelling = expensive and difficult

Question 16

what are the advantages and disadvantages of using 125I?

Answer 16

\:) very high specific activities 
\:) iodination easy
\:) cheap
\:( biological activity of ligand reduced
\:( short half-life 
\:( more readily degraded

Question 17

why do drugs with a low affinity require faster/more efficient separation?

Answer 17

higher rate of dissociation from receptor

Question 18

what is Kd?

Answer 18

dissociation constant

direct measure of affinity of drug

Question 19

how would you measure Kd from a radioligand binding curve?

Answer 19

Kd = concentration at which 50% of the receptors are occupied

Question 20

low Kd = ________ affinity

Answer 20

high

Question 21

what is the scatchard equation?

Answer 21

B/F = (Bmax-B)/Kd

Question 22

what is a scatchard plot used?

Answer 22

• calculate affinity

- calculate number of binding sites

Question 23

in a dose response curve, as the potency of a drug increases how would you expect the shape of the curve to change?

Answer 23

shift to left

Question 24

DEFINE: potency

Answer 24

the amount of drug required to produce an effect of given intensity

Question 25

DEFINE: EC50

Answer 25

concentration of drug required to give 50% of the maximal response

Question 26

why may the response curve be more shifted to the right compared to the binding curve?

Answer 26

signalling through secondary messengers amplifies the response

Question 27

what is the equation for response?

Answer 27

response = max response * [Xa]^n / [Xa]^n + [EC50]^n

Question 28

DEFINE: pharmacokinetic antagonism

Answer 28

reduction in amount of drug absorbed

Question 29

in a dose response curve, as the concentration of an antagonist increases how would you expect the shape of the curve to change?

Answer 29

shift to the right

no change in max or slope

Question 30

describe the schild plot

Answer 30

y axis = log(DR-1)
x axis = log{antagonist]
x intercept = log Kd
straight line

Question 31

what is tachyphylaxis?

Answer 31

desensitisation

Question 32

how may desensitisation of a drug occur?

Answer 32

• internalisation of receptors on cell surface by endocytosis
• change in receptor via phosphorylation –> decreases coupling of receptor to effectors
• exhaustion of mediators
• increased metabolism of drug
• physiological adaptation