Treatment Flashcards
what type of receptor is a nicotinic acetylcholine receptor
receptor-operated ion channel
name the two competitive antagonists to the nicotinic acetylcholine receptor and state which one is reversible/irreversible
reversible:
tubocurarine and vecuronium
irreversible:
(a) bungarotoxin
name two examples of non-competitive antagonists in a nicotinic acetylcholine receptor
lidocaine and tetrodotoxin
what type of receptor is a GABAA receptor
receptor-operated ion channel
to which superfamily of receptors do the adrenoceptor family and the muscarinic acetylcholine receptor family belong
superfamily 2
G-protein coupled receptors
what enzyme is responsible for the turning on and off of a G protein coupled receptor
GTPase
is it GTP or GDP when the G protein is switched on
GTP = on GDP= off
describe the Role of G-proteins and second messengers in Superfamily 2 receptor-effector coupling (how G protein coupled receptors work)
- first messenger
- receptor
- transducer (G protein)
- effector (enzyme or ion channel)
- second messenger (regulate an internal target)
- cellular response
how are second messengers generated within cells
- synthesis inside cell catalysed by enzymes whose activity is regulated by cell surface receptors
or
- influx of ions via channels whose activity is regulated (indirectly) by cell surface receptors
what are the two key protperties of G proteins
Amplification:
- receptor remains active long enough to active several G-proteins (or the same one several times)
- effector remains activated by Ga subunit long enough to generate many molecules of second messenger
Specificity- different Ga subunits (>28):
- each encoded by a different gene or splice variant
what are these effectors regulated by:
- adenylate cyclase (makes cyclic AMP)
- phospholipase C-b (makes IP3 and DAG)
- voltage-gated potassium channels
- voltage-gated calcium channels
effectors regulated by G - proteins
how do allosteric modulators work
allosteric modulators cause shape change in channel protein on binding elsewhere on the protein
This affects properties of gate and influences time for which channel is open (and ions can move)
what do inhibitor modulators do
↓amount of time channel open, ↓ion flux
what do Facilitator Modulator (+ve) do
↑amount of time channel open, ↑ion flux
what are the 5 factors that affect size of response to a receptor agonist
- concentration of drug in vicinity of receptor at a given time - influenced by dose given, route of administration,
distribution throughout the body, rate of elimination
(metabolism, excretion) - affinity - tendency to bind, strength of attraction between agonist and receptor
- ‘intrinsic efficacy’ - ability to activate a shape change leading to response
- nature of receptor-response coupling ‘signal transduction mechanism’
- total number of receptors present
briefly describe receptor occupancy
-Theoretically, size of overall response varies with proportion of receptors occupied by agonist (occupancy)
- maximum response to agonist occurs when all receptors for that
agonist that are present in that tissue are occupied by agonist - proportion of total receptors available which are occupied depends on:
- agonist concentration
- strength of bonds formed
what is the equation of occupancy
Occupancy = [XA]
__________________
[XA] + KA
KA = equilibrium constant* for agonist drug A
what happens when KA = XA in the occupancy equation
occupancy = 50%
KA is numerically equal to the concentration of agonist when half of the total receptors present are occupied
what does an increase and decrease in Ka mean in terms of occupancy
If KA is a very small value (e.g. picomolar, <10-9 M), the bonds formed between an agonist and its receptor are very strong
and it is easier to form complexes but more difficult to reverse or dissociate binding (↑affinity)
If KA is a very large value (e.g. micromolar, >10-6 M), the bonds formed between an agonist and its receptor are very weak and
it is more difficult to form complexes but much easier to reverse or dissociate binding ↓affinity
what is the definition of EC50
EC50 : effective concentration
to produce 50% of maximum response
how is EC50 used
EC50 is a practical, indirect, measure of Drug A’s potency, measured downstream of receptor – relates agonist drug A’s concentration to biological effect produced as a consequence of occupancy
what is intrinsic efficacy
ability of an agonist on binding to a receptor to activate a change in shape or folding of that receptor
what would the typical intrinsic efficacy values be of a full agonist and a partial agonist
full: +1 (or 100%)
- Evoke the maximum shape change/activation response of
which the receptor protein is capable
partial: between 0 and +1
- Evoke less than the maximum shape change/activation
response of which the receptor is capable
briefly describe inverse agonists stating their possible efficacy value
- [-1 < efficacy <0]
- cause –ve shape change which stabilises inactive state of receptor and attenuates coupling/basal activity
- Make receptor less likely to activate signal transduction – negative efficacy value – make it even harder for receptor to be activated