Lecture 6- Neurotransmitters and Receptors Flashcards
What are the three types of neurotransmitters?
- Classical neurotransmission= Small molecule neurotransmitters
- Gaseous neurotransmission= gaseous transmitters
- Neuropeptide transmission= neuropeptides
What type of neurotransmitter is nitric oxide?
Gaseous neurotransmitter
How does nitric oxide word as a neurotransmitter?
- In presynaptic axon terminal Arginine is converted to Citrulline via the catalyst nitric oxide synthase.
- During this process nitric oxide is produced and because this is lipid soluble it can freely diffuse across membranes into neighbouring cells
- The only cells however that it will have an effect on are cells that contain soluble guanylyl cyclase. NO binds to this and causes the breakdown of GTP to cGMP which is a cellular second messenger.
What is required in neighbouring cells for the gaseous neurotransmitter NO to have an effect?
soluble guanylyl cyclase
What is CO and what is it produced by?
- Another gaseous neurotransmitter
- Made very similar to NO but by the heme oxygenase
What is the most common excitatory neurotransmitter?
glutamate
What are the four steps invovled at glutamatergic synapses?
- Synthesis
- Packaging
- Exocytosis
- Recycling
What is invovled in the synthesis phase of glutamatergic synapses?
Glutamine (inactive form) is converted to glutamate by glutaminase
How is glutamate packaged?
Glutamate is packaged into vesicles through vesicular glutamate transporters however this requires going against its concentration gradient (there is already a high concentration of glutamate inside). Therefore ATpase is required which breaks down into Hydrogen and ADP + P (releasing energy).
How is glutamate exocytosed?
The vesicles merge with membrane of presynaptic vesicle either via full fusion or kiss and run. Glutamate crosses the synaptic clef and binds to glutamate receptors in the post synaptic cell membrane in order to have their effect.
Why don’t we want glutamate sitting in the synaptic clef for longer than it is needed and what is the solution to this?
would
- Would get endless activation.
- To prevent this glutamate is recycled. It is taken up into glial cells by excitatory amino acid transporters 1+2. Glutamate is then synthesized back into glutamine (inactive version) via glutamine synthase and this glutamine travels back into the presynaptic terminal ready for the process to start again.
How do excitatory amino acid transporters work to get glutamate into glial cells (during recycling)?
Because glutamate would have to go against its concentration gradient the process is coupled with ions (sodium and hydrogen). Chloride is also invovled.
What do glutamate receptors consist of?
3 transmembrane domains, 4 subunits (alpha, beta, gamma, delta)
What does changing the composition of the glutamate receptor subunits do?
It alters and changes the responses you can get
Assertion question:-
Gaseous neurotransmitters act on receptors in the synaptic cleft
BECAUSE gaseous neurotransmitters freely diffuse across the cell
membrane.
Answer:-
A. if both statements are true, and the second causes the first.
B. if both statements are true but the second does not cause the first.
C. if the first statement is true and the second is false.
D. if the first statement is false and the second is true.
E. if both statements are false.
D.
What are the two types of receptor present on the post-synaptic membrane utilized in classical neurotransmission?
Ionotropic and G-protein coupled receptors
How do ionotropic receptors work?
- Neurotransmitter binds to a receptor
- This receptor also acts as an ion channel which becomes open upon binding
- Ions then flow across the membrane down their concentration gradient and can modulate the resting membrane potential
What is another word for the neurotransmitter that binds to the ionotropic receptor?
Ligand
What are g-protein coupled receptors also called?
Metabotropic receptors
How do G-protein coupled receptors work?
- A neurotransmitter binds to a membrane receptor
- This causes G-protein subunits (alpha, beta, gamma) to become activated
- These protein sub units directly or Intracellular messengers (2 step- effectors) modulate the activity of ion channels to open them
- Ions then flow across the membrane down their concentration gradient (either in or out) and effect the membrane potential
What requires the use of a G-protein coupled receptor?
Acetylcholine, biogenic amines, neuropeptides, purines
What are cys-loop receptors made of?
- Four transmembrane domains
- 5 subunits (again composition alters what ions we can transport and therefore the response we get)
Are cys-loop receptors all excitatory?
No some are excitatory, some are inhibitory depending on selectivity
