Ionotropic And Metabotropic Receptors Flashcards
What are metabotropic receptors ?
Coupled to intracellular proteins which transduce the signal to the cell interior
7 transmembrane domains
Single subunit
Effects are longer lasting as they activate 2nd messenger systems
What are ionotropic receptors ?
Ligand gated ion channels
Form an ion channel that’s allows the passage of ions which either depolarises or hyperpolarises the cell
What is current ?
Measure ion flow
If the flow is inwards then it produces a downward deflection and if it is outward it produces an outward deflection
If you get an inward positive current what happens to the postsynaptic potential ?
Excitatory potential which becomes more positive creating a upward deflection
What is temporal summation ?
Activating the same synapse with EPSPs in quick succession - combining of EPSPs helps to produce an action potential
What is spatial summation ?
This is when a neurone is activated by more than one PSP
What is another name for ionotropic acetylcholine receptors ?
Nicotinic acetylcholine receptors because nicotine is an agonist to them
What is the general structure and function of nicotinic acetylcholine receptors ?
5 subunits- 2-alpha, beta, gamma and delta
- has to have 2 alpha subunits to bind the 2 acetylcholine molecules
- each subunit has 4 transmembrane domains
- 1 of these domains always faces inwards and it is the amino acid helix of this which determines which ions can pass through
Form a complex with a pore that’s closed at rest
Binding of acetylcholine causes pore to open for <1ms to allow ions through - sodium and potassium
Which domain of each subunit in nicotinic acetylcholine receptor faces into the channel ?
Domain 2 - the negatively charged amino acids form the selectively filter
What happens to nAChR when the concentration of acetylcholine increases ?
Increases the number of times the channels open
Increases the length of time the channels are open
What are the subunits for nAChR in muscle ?
2 alpha, beta, delta, gamma or epsilon - gamma or epsilon is dependent upon the stage of development
Binds alpha- bungarotoxin
What subunits for nAChR are present in the brain ?
Either 3 alpha and 2 beta or 5 alpha
Mostly doesn’t bind alpha- bungarotoxin
What effect does changing the subunits of an ionotropic receptor do ?
It alters the properties of the channels
What are the ionotropic receptors for glutamate ?
AMPA
Kainate
NMDA
Each of these receptors have a variety of subunits to alter the properties
What are NMDA receptors important for ?
Learning and memory
What are AMPA receptors important for ?
Most important for glutamate excitation
When lots of synaptic activity occurs it is these receptors which activate he NMDA receptors
What are kainate receptors important for ?
They seem to have an involvement in epilepsy
How many subunits for glutamatergic receptors have ?
4 they are tetramers
What are the types of AMPA receptors ?
GluR1 + GluR2 which is the most common type, allowing only sodium and potassium ions through
GluR1 + GluR1 which also allows calcium through
- these are unregulated when there is lots of synaptic activity and the ability to let calcium through means there is a larger depolarisation and the response lasts longer because it can act as a second messenger
What is the structure of an NMDA receptor like ?
2 NR1 subunits - binds glycine
2 NR2 subunits - bind glutamate
Allows sodium potassium and calcium ions through
Rest it’s blocked by magnesium ion preventing the passage of any ions
What can ions flow through NMDA receptors ?
Only if there has been sufficient depolarisation by AMPA receptors to inhibit the driving force of the magnesium ion so that it leaves the channel
If another action potential occurs then it will be open to allow the passage of ions
Enable flow at high frequencies
What is an example of an antagonist for AMPA/kainate receptors ?
NBQX
What is an example of an antagonist for NMDA receptors ?
APV
What are GABAa receptors like ?
Ionotropic
Allow chloride through
Causes hyperpolarisation
Have many modulatory binding sites which alter the effects of GABA binding
Which acetylcholine receptors are more prominent in the brain ?
Metabotropic
What are the metabotropic acetylcholine receptors like ?
5 types of receptors
1,3 and 5 are coupled to PLC
2 and 4 are coupled to adenyl Cyclase
What are the metabotropic glutamate receptors like ?
8 different ones
Class 1 = 1 and 5 - coupled to PLC
Class 2 = 2 and 3 - decrease cAMP
Class 3 = 4, 5, 6, 7 and 8 - autoreceptors
