Molecular Pharmacology - Synaptic Receptors Flashcards
what are the features of dendrites
input - afferent
short and multiple processes
markers - MAP2
postsynaptic spines
what are the features of axons
output - efferent
thinner and longer than dendrites
markers - Tau
postsynaptic terminals
function of basket cells
they target alpha-1 receptors
regulate the generation of action potentials from pyramidal neurones in layer 5
what is an experimental method to study heterologous receptors using HEK cells
transfect the HEK cells with plasmids carrying the sequence of interest and a fluorescent marker (GFP)
wait ~3 days for expression and membrane insertion of protein channels
what is an experimental method used to study heterologous receptors using oocytes
microtransplantation:
take human tissue - extract the mRNA of interest
inject said mRNA into xenopus oocyte
wait for expression to study receptor of interest
outline the brain slice technique
brain is rapidly extracted and sliced in ice-cold cerebrospinal fluid
slices survive for up to 12 hours
what are the pros of the brain slice technique
network connectivity is preserved
anatomically identifiable regions
allows for single cell recording and identification of cells
what glutamate receptors are responsible for fast excitation
AMPA
Kainate
what glutamate receptor is responsible for coincidence detection
NMDA
what are iGluR
selective cationic channels
what is the reversal potential for cationic channels in neurones
0mV
what happens when cationic channels in neurones open
the cell depolarises - brings the cell closer to threshold
- generates excitatory effect
what is permeability of all ion channels dictated by
the ion channel molecule
what is decay time
how long does the receptor hold onto the neurotransmitter
what is the decay time for AMPA and NMDA
AMPA - 3ms
NMDA - 40-2000ms
where is the C-terminus of GABA receptors located (AMPA/NMDA)
located intracellularly
important for scaffolding and function
what is the overall structure of glutamate receptors
3 transmembrane domains
1 reentrant loop
intracellular C-terminus
extracellular N-terminus
ligand binding domain is made from N-terminus region S1 and S2
what is required for AMPAR activation
binding of one glutamate to subunit to open the AMPA pore
conductance (g=I/V) is agonist dependent
what is required for NMDAR activation
2 molecules of glutamate must bind to GluN2 subunits
2 molecules of glycine - co-agonist - must bind to GluN1 subunits, D-serine can also serve this function
conductance of NMDAR is agonist independent
what does conductance mean
if something’s conductance is agonist dependent then the amount of agonist influences the degree to which the receptor/pore is activated/opened and vice versa for independent
outline the conductance of AMPA
so there are 4 subunits to AMPA, each with a glutamate binding site
if one glutamate is bound then 1 quarter of the pore is open, the more glutamate bound to each unit the more the pore opens
what is the S1 and S2 regions connected by
a glycine-threonine linker
why are NMDAR voltage dependent
because of Mg2+ blockade
what do NMDAR act as
coincidence detectors after repetitive stimulation
permeate Ca2+ into the neurone - activates many secondary messengers
what is present on the GLUA2 sequence that codes for one of the glutamate receptor domains
codes for the reentrant loop
Q/R is present in the sequence
present in the pore lining
dictates permeability of the pore
what is the feature of GLUA2 lacking AMPAR
is Ca2+ permeable
inwardly rectifying conductance
high-single channel conductance
fast deactivation time
what are TARPs
Transmembrane AMPAR Regulatory Proteins
different subtypes: gamma1-gamma8
y2 is known as stargazin
they effect trafficking and function
what is necessary for the super-activation of glutamate receptors
the concerted action of L1 and L2 extracellular loops on TARPs
what is the obligatory subunit of NMDA receptors for their expression
GluN1
during development, which NMDA subunit is most prominent
GluN2B
when does GluN2A expression increase
in adults
what does Glun2B contain
a PDZ binding domain
what is the function of a PDZ binding domain
binds to PSD-95 and promotes synaptic localisation
for GABA receptors in maturing and adult physiology, what is the mM of Cl- inside and outside cell
outside - both 110mM
inside maturing - 30mM
inside adult - 5mM
for GABA receptors in maturing and adult physiology, what voltage does the membrane want to rest at and why
adult = -82mV
maturing = - 34mV
caused by the distribution of Cl-
what leads to the difference in internal Cl- mM from maturing to adult
KCC2 becomes more efficient at exporting Cl- to outside the cell as the physiology matures
what are the features of GABA receptors
fast inhibition
tonic inhibition
how many transmembrane domains do metabotropic receptors have
7
what type of receptors are metabotropic receptors
Class C GPCR
what is each subunit of metabotropic receptors made from
made from an extracellular venus fly trap domain (VFTD) that binds agonists and links to the 7 transmembrane domains
what are mGlu receptors
homodimeric receptors - 2 metabotropic receptors
what is required to form i dimer for mGlu formation
intramolecular disulfide bridges in both VFTDs
what is required for mGluR activation
efficient signalling - glutamate binds to both VFTDs
can also activate from just one glutamate to one VFTD but less efficient
which mGlu5R subtypes are more predominant during postnatal period and adulthodd
mGluR5a - postnatal period
mGluR5b - adulthood
what is mGluR5
a group 1 receptor - mostly postsynaptic
can form homo/heterodimers
what is the function of mGluR5
regulates mechanisms in neurogenesis and synaptic regulation
what can disregulation of mGluR5 cause
Fragile X syndrome
autism
schizophrenia
Alzheimer’s
what do distinct binding pockets of for NAMs in Glu1 and Glu5 reveal
that multiple sites in class C 7TMDs can bind allosteric regulators
what can mGlu5 antagonists do
restore amyloid-beta inhibited LTP to normal levels
what is the pathology of fragile X syndrom
mGlu5R activation is way too much
leads to way to much translation machinery being activated - transcribes mRNA into too many proteins that cause too much endocytosis of AMPA receptors - too few AMPA receptors are expressed on the surface
what is the function of FMRP
inhibits translation machinery from transcribing mRNA - pivotal for preventing Fragile X syndrome
what can GABAb receptors modulate
modulates the firing rate of basal ganglia neurons in the brain
what is the structure of a GABAb receptor
GABAb1a - contains 2 N-terminal sushi domains (SD) - axonal localisation
GABAb1b - dendritic localisation
what are the functions of the GABAb subunits
GABAb1a - contains the VFTD agonist binding site
GABAb1b - couples to the G-protein
what are the functions of dopamine releasing neurones in the basal ganglia
steady, autonomous pacemaking
self-generated mechanism maintains extracellular dopamine levels
how does GABA what can GABAb receptors form
supercomplexes - when heterodimers self-assemble into tetramers or oligomers
how are supercomplexes formed
via interactions of the VFTD on GABAb1a
what would happen if you applied a GABAb antagonist to dopamine releasing neurones in the basal ganglia
they inhibit it
the graph of activity goes silent
what does GABAb lack
lacks a cysteine-rich domain - its more compact
in terms of activation what is the difference between GABAb and mGlu heterodimers
GABAb only requires one agonist per dimer for full activation
what are KCTDs
K+ channel tetramarisation domains
are GABAb receptor components that act as auxillary receptor subunits
they are not K+ channels
they help GABAb link with other proteins
what are the core building blocks of GABAbR
GABAb1a
GABAb1b
KCTD
G-protein
