Glutamate and Anaesthesia Flashcards
How can we see the function of glutamate receptors in cell lines?
Typically you would transfect cells which do not express these receptors
And apply pulse of agonists
Use whole cell voltage clamp recordings of the cell
Can be done for AMPA, NMDAR and kainite too
Why does Mg2+ block the NMDAR?
Positive charge attracted to the negative membrane potential
What do NMDARs conduct?
Ca2+
K+ in the opposite direction
What can blockage of NMDAR cause?
Psychotic state
ie with ket and PCP
In addition to glutamate, what else does the NMDAR require to stay open?
A coagonist - glycine or D-serine
How do we know that NMDAR activation requires agonist and coagonist binding?
From whole cell voltage clamp recordings
Noted that in the absence of glycine, glutamate current is not persistent as it does not activate NMDARs
Where does glutamate bind to the NMDAR?
GluN2 subunit
Where does glycine bind to NMDAR?
GluN1 subunit
How do we know that Mg2+ blocks slow NMDAR transmission?
Measurement of NMDAR EPSCs in neurons
Cells in solutions containing Mg2+ only demonstrate a fast EPSC which is dampened by a AMPA antagonist (CNQX)
In Mg2+ free solution the EPSCs have a slow and a fast component
The CNQX here has no affect on the slow component
Which part of the glutamate receptor is the part which makes up the ion channel?
TM2
What are most GluA2 subunits edited to in an adult?
GluAR
GluAR is calcium impermeable
T/F
True
GluA1,3,4 and unedited GluA2(Q) are calcium permeable
What is the edit made in GluA2?
Adenosine to arginine in the TM2 re-entrant loop
Q607R
Why don’t polyvalent cations (such as spermine) block GluA2R?
It is positive so is repelled by the positive charge of arginine
What do AMPARs mediate?
Fast synaptic transmission
What is the difference between the function of edited and non-edited AMPA subunit GluA2?
Q - calcium permeable and blocked by internal polyamines
R - calcium impermeable, not blocked by internal polyamine and reduced single channel conductance
What shape of structure do the S1 and S2 domains take on the AMPAR?
Clamshell structure which shuts when bound
Which subunits are most NMDARs made from?
GluN1 and GluN2
What is there in the NMDAR equivalent of Q/R site?
Asparagine (N)
site of Mg block
What does IV ketamine induce?
A dissociative state with marked sensory and memory loss
Without complete LOC
Describe the effects of ketamine on GABAa receptors?
(Little to) none
How does ketamine affect NMDAR?
Voltage dependent block
What is the state of the NMDA channel when ketamine applied?
Equilibrium between bound and open (ar) and open but blocked (2ard)
What “anaesthetic” competes with glycine for the co-agonist site on the GluN1 subunit?
Xenon
What is normally used for the induction of anaesthesia and why?
IV drugs
Propofol, etomidate, thiopental
They produce a state of unconsciousness within 20 seconds
What is used for maintenance anaesthesia?
Inhalational agents
Like isoflurane or sevoflurane
Or continuous propofol
What is the main difference between nitrous oxide and isoflurane?
Isoflurane acts on GABA
Nitrous oxide doesnt
Outline AMPAR trafficking in and out of the postsynaptic density
Newly made recs transported in vesicle by molecular motors on microtubules
Exocytoses into dendritic shaft (then moves randomly at cell surface)
Stabilised by diffusion trapping via interactions with scaffold proteins
Diffusion receptors internalised at the extrasynaptic endocytic zones by clarithirin dependent endocytosis
These are then recycled back by exocytosis or tagged for breakdown
What may cause AMPAR trafficking?
Neuronal activity
Stress hormones
Neurodegen disease
Drugs
Which drugs may cause AMPAR trafficking?
Ketamine
Cocaine
Tianeptine
How can LTP be induced?
High frequency theta burst stimulation of the Schaffer collateral pathway from CA3
What induces LTD?
Repetitive LFS
Which is associated with an increase in synapse number?
LTP or LTD?
LTP
What occurs with stabilising AMPARs in the synapse?
Interactions of C terminus and various interactor proteins
Which ampakine may increase QoL in HD?
CX929
Improves LTP in mutant huntingin and improves cognition and performance in NOR in CAG140 mice
(Nekooki-Machida 2009)
Ketamine acts on NMDAR, the metabolite HNK acts on…
AMPAR
How do we know this is the receptor where HNK works?
Administration of ketamine and metabolite and monitored the EPSCs of the different receptors
