pharmacology Flashcards
how many TM domains do ligand gated ion channels have?
4 or 5
what does protein kinase A do?
phosphorylate proteins on serine and threonine residues which have a hydroxyl group
what does arrestin do?
binds to g-protein coupled receptors and arrests their function + stops signalling
involved in desensitisation
describe the g protein signalling cascade
- agonist binds to G-protein coupled receptor
- receptor undergoes conformational change —> activates g protein
- α subunit unbinds to β and γ subunit
- α subunit bind GTP —> activates
- α subunit activates downstream signalling pathway
describe the signalling pathway activated by Gs α subunit
- α subunit activates adenylyl cyclase
- adenlyl cyclase converts ATP to cAMP
- cAMP activates PKA
describe the signalling pathway activated by the Gi α subunit
α subunit inhibits adenylyl cyclase
describe the signalling pathway activated by the Gq α subunit
- α subunit activates phospholipase Cβ
2. phospholipase Cβ breaks down PIP2 to produce IP3 and DAG
what is the purpose of the βγ subunits in G proteins?
regulates gating of certain ion channels
DEFINE: affinity
measure of how well the drug and ligand bind each other. fast forward reaction and slow backward reaction.
DEFINE: occupancy
measure of how many receptors are occupied by drugs and forming drug-receptor complexes
DEFINE: efficacy
the ability of a drug to produce a maximum response
how would you reduce non-specific binding to filters and glass?
anti-absorbants
e.g. albumin or collagen for peptides
O-catechol for catecholamines
radioligand binding assay
- 1st set of tubes = tissue + radioactive ligand
bound radioactivity = specific binding + non-specific binding - 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 - specific binding = total bound - non-specific binding
how to avoid degradation of ligand?
- 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
what are the advantages and disadvantages of using 3H?
:) labelled product indistinguishable from native compound
:) stabile
:) long half-life
:) high specific activities can be obtained
:( specialised labs required
:( labelling = expensive and difficult
what are the advantages and disadvantages of using 125I?
\:) very high specific activities \:) iodination easy \:) cheap \:( biological activity of ligand reduced \:( short half-life \:( more readily degraded
why do drugs with a low affinity require faster/more efficient separation?
higher rate of dissociation from receptor
what is Kd?
dissociation constant
direct measure of affinity of drug
how would you measure Kd from a radioligand binding curve?
Kd = concentration at which 50% of the receptors are occupied
low Kd = ________ affinity
high
what is the scatchard equation?
B/F = (Bmax-B)/Kd
what is a scatchard plot used?
- calculate affinity
- calculate number of binding sites
in a dose response curve, as the potency of a drug increases how would you expect the shape of the curve to change?
shift to left
DEFINE: potency
the amount of drug required to produce an effect of given intensity
