Major Receptor Families Flashcards
What is the richest source of receptors
Membrane bound proteins
What are the 4 majour families of receptors
1) Ligand- gated ion channels (eg. Cholinergic ion channels)
2) G- protein coupled receptors (eg. a and B receptors)
3) enzyme- linked receptors (eg. Insulin receptors)
4) intracellular receptors (eg.steroid receptors)
How do transmembrane ligand gated ion channels work
The channel is always closed until it is bound to an agonist then is is open for a few seconds
What does the response of an ion gated channel depend on?
The ions conducted through the channels
What does stimulation of nicotinic receptors lead to
By stimulation with acetylcholine channels open allowing the influx of sodium and Efflux of potassium across the cell membrane generating an action potential
What happens after the activation of GABA receptors
Cl- influx resulting in hyper polarisation
What happens when a local anaesthetic binds to voltage gated channels
Inhibition of ana+ influx and decrease in neuronal transmission
How do G protein coupled receptors work
They are composed of 3 subunits, a subunit binds to GTP and B and y anchor the G- protein in the cell membrane, what an agonist binds to the G protein causes the increase in GTP binding to a subunit causing dissociation of the a-GTP complex and By complex’s, these complexes are then free to interact with cellular effectors
What are the subtypes of G-proteins
Gs
Gi
Gq
How does Gs work
Gs - activates adenylyl cyclase -> increases camp
How does Gi G protein work
Gi inhibits adenylyl cyclase -> decreasing camp
How does Gq G protein work
Gq - activates phosphlipase C -> generating IP3 and DAG
What does IP3 from Gq do
IP3 increases cellular calcium —> activating protein kinase
How does DAG from Gq work
DAG similar to CAMP activates specific protein kinases
a1,a2,B1,B2
QISS
M1,M2,M3
QIQ
How long does G protein channel last
Several seconds to minutes
How long does enzyme linked receptors last
Minutes to hours
What do the most common enzyme linked receptors have
Tyrosine kinase
What’s the mechanism of action of enzyme linked receptors
Phosphorylation of tyrosine residues with the help of tyrosine kinase in turn activate phosphorylates target protein creating a cascade similar to G proteins
How does the ligand reach intracellular receptors
It must have enough lipophilictiy to pass through the cell membrane
What is the primary target of activation of intracellular receptors
Transcription factors in the nucleus
How long does it take for intracellular receptors need to show their activity
Hours to days
What is signal amplification characteristic of
Enzyme linked receptors and G protein coupled receptors
What is the result of signal amplification
Not all receptors need to be bound in order to elicit a maximal response
What are spare receptors and give examples of them
Systems which don’t need to bind to all receptors in order to elicit a maximal response are said to have spare receptors
Eg. 5-10% of B receptors in the heart are spare
99% of insulin receptors are spare
Why does desensitisation occur
Due to too much agonists activity resulting in diminished response
What is tachyphylaxis
Another name for desensitisation and it occurs due to phosphorylation causing receptors unresponsive to agonists
What does too much agonistic activity lead to
Down regulation
What does too much antagonist activity lead to
Up regulation can make cells more responsive to agonist and less to antagonist
What is a refractory period
After receptors activation, some receptors (i.e ion channels) require some time before they get activated again
