Download - GABA and GABA receptors
-
8/3/2019 GABA and GABA receptors
1/18
1
Presynaptic terminalGlial
Postsynaptic neuron
2
GABA and GABA receptors
Lecture 1. GABAA receptors
Lecture 2. GABAB receptors
Lecture 3. GABA homeostasis
Lecture 4. Modulation of GABAergic
synaptic transmission
-
8/3/2019 GABA and GABA receptors
2/18
3
What is GABA?
Inhibitory neurotransmitter.
~1/3 of synaptic transmission in the brain is mediated by
GABA.
Neurons that synthesize and release GABA is called
GABAergic neurons.
-aminobutyric acid
4
GABA receptors
GABAA receptors
Ligand-gated ion channels
Fast synaptic inhibition
GABAB receptors GTP-binding protein coupled receptors
Slow synaptic inhibition
GABAC receptors
-
8/3/2019 GABA and GABA receptors
3/18
5
molecular structures
location and function
single channel recording
pharmacology
two types of inhibition
Lecture 1. GABAA receptors
6
Benzodiazepines
Barbiturates
Neurosteroids
Anesthetics
-
8/3/2019 GABA and GABA receptors
4/18
7
GABAAR is ligand-gated ion channel
Cytoplasmic side
Extracellular side
ChannelPoreReceptor
Transmitter
Gate
8
Molecular structure of GABAA receptors
1-3
Moss & Smart
2001
-
8/3/2019 GABA and GABA receptors
5/18
9
subunits are part of GABAA receptor family
1-3
Moss & Smart
2001
Dendrogram of the deduced amino
acid sequences of GABAAR subunits.
from Cherubini and Conti 2001
structure
functionpharmacology
10
Distribution of GABAAR -subunit
mRNA in rat brain
-
8/3/2019 GABA and GABA receptors
6/18
11
Multiple subunits: 16, 13, 13, , , , ,13
Each subunit contains 4 putative
transmembrane domains, TM2 is believed to
form the lining of the channel.
Hetero- or homo-oligomeric proteins.
Pentamer with ::at a ratio of 2:2:1
subunit composition determines functionalproperties and pharmacology.
Molecular structure of GABAA receptors
12
Location
Cl-
Presynaptic terminal
Glial
GABA RA Postsynaptic neuron
Synaptic cleft
IPSP
Cl- and HCO3-
-
8/3/2019 GABA and GABA receptors
7/18
13
Nernst equationCl
10 mM
-
Cl125 mM
-
E =ClRT [Cl]o
zF [Cl]iln
E =Cl[Cl]o[Cl] i
log-60
E =Cl -66 mV
z = charge of diffusible ion (Cl- = -1)
R = universal gas constant
T = absolute temperature
F = Faraday's Constant
14
recordingrecording
Inhibitoryinterneuron Motor
neuron
Currentpassing
Currentpassing
AP
IPSP
-
8/3/2019 GABA and GABA receptors
8/18
15
Reversal potential of IPSP
-55
-35
-74
-99(mV)
E -Cl
Postsynaptic
potential
Postsynaptic
current
Clflux
-
Current clamp Voltage clamp
16
IPSP reduces cell excitability
Membrane
hyperpolarization
drive membrane potential
away from the threshold
potential.
Reduction in membrane
resistance
reduce the excitatory input.
This is known as shunting
inhibition.
Threshold potential
Threshold potential
E -Cl
E -Cl
-
8/3/2019 GABA and GABA receptors
9/18
17
Single channel recording
GABA
Closed Open BoundBoundBound Open Closed
Open
Closed
18
ligand binding sites on GABAA receptors
benzodiazepine
picrotoxin
-
8/3/2019 GABA and GABA receptors
10/18
19
GABAA receptor pharmacology
Agonists GABA, muscimol
Antagonists Bicuculline, picrotoxin,
gabazine
Modulators Zn2+
Neurosteroids
Benzodiazepines
Anesthetics
Barbituates
Alcohol
101 1000
100
0
Response(%)
Dose
50
100
0
Response(%)
Dose
50
100
0
Respon
se(%)
Dose
50
KD
Maximum Response
affinity
affinity
efficacy
efficacy
101 1000100
101 1000100
20
Phasic and tonic inhibitions
high agonist dose ~1
mM
quantal release
Action potential-
dependent IPSPs
Action potential-
independent mIPSPs
synaptic receptors
sensitive to gabazine
low agonist dose ~1M
unknown mechanisms
reverse uptake
spill over
extracellular matrix
channel spontaneous
open
extrasynaptic receptors
insensitive to gabazine
20 pA
40 ms
Bicuculline
50pA
1 min
-
8/3/2019 GABA and GABA receptors
11/18
21
GABAAR and disease
GABAAR is a major target for developingtherapeutics. pain
epilepsy
anxiety
depression
sleeping disorders
Mutations in GABAARs are found to be linked to
epilepsy.
22
GABAAR Summary
GABA-gated anion channels.
The primary inhibitory receptors in themammalian brain.
Pre-, post-synaptic and extrasynaptic area,mediating inhibitory postsynaptic potentials
(IPSPs) and tonic inhibition. Important targets for therapeutic agents.
Mutations in the genes encoding GABAAreceptor subunit correlate with certain type ofepilepsy.
-
8/3/2019 GABA and GABA receptors
12/18
23
Questions
24
Lecture 2. GABAB receptors
molecular structures
location and function
modulation
-
8/3/2019 GABA and GABA receptors
13/18
25
GABABRs are G-protein coupled receptors
Extracellular side
Cytoplasmic side
NH2
COOH
ReceptorTransmitter
PPP
GTP
G protein
P
Channel
Gate
26
Molecular structure of GABAB receptors
Heterodimer linked
by coiled-coil
domain
GABAB1a-f
GABAB2, 35%
homology withGABAB1
coupled to Gi/Go
Marshall, FH et al, 1999
-
8/3/2019 GABA and GABA receptors
14/18
27
Function of GABABRs
PPP
GTP
Ca K2+ +
GABA RB
Adenylyl cyclase
28
GABABRs - postsynaptic
GABA RB
fast IPSP
slow IPSPE
E
Cl-
K+
-
8/3/2019 GABA and GABA receptors
15/18
29
GABABRs - presynaptic
GluRs
EPSP
Threshold
GABA RB
GABA RsA
IPSP
GABAergic Glutamatergic
GABA RB
30
GABABR function
opening K+ channels in the postsynaptic
membrane.
closing Ca2+ channels in the presynaptic
terminal.
GABAergic: autoreceptor
glutamatergic: heteroreceptor
-
8/3/2019 GABA and GABA receptors
16/18
31
GABABR pharmacology
Agonists GABA, (-)baclofen, APPA
Antagonists
saclofen, phaclofen, CGP35348, CGP55845A
Modulators
CGP7930
32
GABABR and disease
GABABR agonist
antispasticity
antinociceptive
suppression of drug craving
GABABR antagonist
suppress absence seizure in animal models
-
8/3/2019 GABA and GABA receptors
17/18
33
GABABR Summary
G-protein coupled receptors.
Heterodimer with GABAB1 and GABAB2.
Mediate slow IPSP via opening K+ channel at
postsynaptic membrane.
Decrease synaptic release via inhibit Ca2+
channels in the presynaptic terminal.
targets for therapeutic agents.
34
Function of GABAARs and GABABRs
Under several conditions GABAR-mediated response can be excitatory. GABAARs
EIPSC higher than the threshold (Cl- or HCO3
-).
Disinhibition
GABABRs Presynaptic inhibition on inhibitory neurons
Activating K+ channel may recruit T-type Ca2+
channel to induce oscillation in thalamus.
Disinhibition
-
8/3/2019 GABA and GABA receptors
18/18
35
Reference books
Principles ofneuroscience
4th Edition
Eric R. Kandel
Jame H. Schwartz
Thomas M. Jessell
New York: Elsevier
From neuron tobrain
4th Edition
John G. Nicholls
Robert Martin
Bruce G. Wallace
Paul A. Fuchs
Sunderland: SinauerAssociates