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physiology and pharma > L8 - Amino Acid transporters > Flashcards

L8 - Amino Acid transporters Flashcards

1
Q

what determines whether an AP is fired?

A

whether the summation of EPSPs and IPSPs (temporal and spatial) reaches the threshold for an AP (-55mV)

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2
Q

what effect does glutamate have when acting on ionotropic receptors

A

excitatory (fast acting)

opening of Na+ / K+ channels (equally permeable)

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3
Q

what effect does glutamate acting on metabotropic receptors havve

A

slower acting inhibitory effect (increase IPSPs) (presynaptic inhibition and modifying frequency of postsynaptic APs)

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4
Q

what effect does GABA have when acting on
ionotropic
metabotropic
receptors

A

inhibitory effect on both

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5
Q

what effect does glycine have and what type of receptor does it act on?

A

inhibitory
ionotropic

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6
Q

where is glutamate synthesised? and why is this important

A

synthesised in brain from glucose metabolism
or from glutamine in astrocytes

important as glutamate cant cross BBB

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7
Q

what is the name of the vesicular glutamate transporters

A

VGluT 1-3

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8
Q

how is a concentration gradient maintained for the transport of NT into vesicles?

A

H+ ATPase actively pumps H+ into vesicles
each NT transporter can then use this [H+] gradient to transport NT into vesicles via antiport

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9
Q

how is Gutamine transported into glial cells?

A

EAAT (transporter)
using co transport of 2Na / 3H+ into glial cell
or counter-transport of K+

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10
Q

what are the three classes of ionotropic glutamate receptors

A

NMDA
AMPA
Kainate

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11
Q

what are the NMDA receptor channels permeable to

A

Na+
K+
Ca2+

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12
Q

what are the AMPA receptor channels permeable to

A

all permeable to Na+ / K+
some permeable to Ca2+

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13
Q

what are kainate receptor channels permeable to?

A

Na+
K+
Ca2+

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14
Q

where are kainate receptors mostly found

A

pre-synaptically - modulate NT release

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15
Q

how many subunits are there for the AMPA receptor (name them) and how do they exist in the receptor

A

4
GluA1-4

receptor is a tetramer

subunits exist in pairs, so the receptor will be 2x one type and 2x another type (eg 2x GluA1 and 2x GluA2)

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16
Q

how many subunits does the NMDA receptor have (name them) and how do they exist in the receptor (how many of each type)

A

5
GluN1
GluN2 (A-D)

receptor is a tetramer
subunits exist as 2x GluN1 then 2x any of the GluN2 subunits

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17
Q

how many subunits does the Kainate receptor have (name them) and how do they exist in the receptor (how many of each type)

A

5
GluK1-5

tetramer
GluK1-3 can form homomeric receptors, or can combine with 2x another subunit (always pairs)

GluK4-5 have to combine with 2x GluK1-3 (2+2) to be functional

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18
Q

where in brain are AMPA and NMDA receptors found

A

the different subunit types can be found in diifferent brain regions but AMPA and NMDA are generally found at the same functional excitatory synapses

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19
Q

why is GluN1 expressed in all brain regions?

A

because a fucntional NMDA receptor must have 2x GluN1 subunits

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20
Q

describe the speed of activation and inactivation of AMPA receptors

A 
fast acting (fast depolarisation) 
fast decay (inactivation)
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21
Q

why is the AMPA receptor fastly inactivating?

A

due to relatively low affinity for Glutamate

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22
Q

describe the speed of activation and inactivation of NMDA receptors

A

slower activating
slower inactivating

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23
Q

why is the NMDA slower inactivating than the AMPA

A

NMDA has a higher affinity for glutamate - glutamate stays bound for longer so the channel may open and close several times before glutamate dissociates

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24
Q

why is the NMDA receptor slower activating?

A

its voltage sensitive

at membrane potentials more negative than -50mV, the channel opens but is blocked by a Mg2+ ion (trying to flow into the negative cell as its positive)
as the membrane becomes more depolarised (-40mV) the Mg2+ is less attracted and so the channel is unblocked

25
what is the significance of the slower activating NMDA receptor
allows summation of non-synchronous inputs (not arriving at same time) multiple inputs are required to relieve the Mg2+ block - so AMPA receptors can sense activity of many synaptic inputs on one cell
26
what subunit of the NMDA receptor does glutamate bind what other binding is required for this receptor to be activated?
GluN2 glycine binding to the GluN1 subunit
27
describe the EPSPs of kainate receptors
relatively long lasting (similar to NMDA), only seen at few synapses
28
what effect does Kainate receptor activation have?
presynaptically -\> modulates NT release post synaptically -\> increase excitability of neurones via unknown G-Protein mechanim
29
how many types of Glutamate metabotropic receptors are known
8 grouped into 3 subgroups
30
what are the 3 subgroups of mGluRs and what G protein are they coupled to
**Group 1** (mGluR1 &5) → (Gq) Group 2 (mGluR 2&3) → Gi/Go Group 3 (mGluR4,6,7,8) → Gi/Go
31
describe the group 1 mGluRs (what types included, what G protein coupled to and what is their function
**Group 1** (mGluR1 &5) (Gq) -\> alpha subunit activates phospholipase C producing DAG and IP3, * IP3 triggers Ca2+ release (from ER/SR) increasing intracellular [Ca2+] * DAG activates PKC which can then phosphorylate proteins By subunit modifies ion channel activity
32
describe the group 2&3 mGluRs (what types included, what G protein coupled to and what is their function
Group 2 (mGluR 2&3) → Gi/Go Group 3 (mGluR4,6,7,8) → Gi/Go all have the same function → * a subunit inhibit adenylyl cyclase decreasing cAMP levels * by subunit mmodifies ion channel activity
33
what are the mGluRs grouped according to?
AA sequence agonist pharmacology signal transduction pathways
34
what effect does the By subunit of g protein linked mGluRs have pesynaptically
inhibit VGCC opening (less NT release) interact with exocytosis mechanims to inhibit NT release
35
what effect does the By subunit of g protein linked mGluRs have postsynaptically
modify K+ channel activity (opening them) causing hyperpolarisation
36
where in the body is GABA found
brain pancreas no where else in body at significant concentrations
37
describe GABA synthesis
glutamate → GABA via GAD(glutamic acid decarboxylase)
38
describe degradation of GABA
GABA → succinic semialdehyde via GABA transaminase
39
describe function of vigabratin
irreversibly inhibits GABA transaminase causing increased GABA levels
40
name the vesicular GABA transporters
VIATT (also for glycine)
41
describe reuptake of GABA
1. into astrocyte via Na cotransport where its degraded 2. uptake into presynaptic terminal where its reused 3. uptake into postsynaptic neurones where its destroyed
42
where are ionotropic GABA(A) receptors found
post synaptically
43
describe the structure of the (ionotropic) GABA(a) receptor
5 subunits (2a, 2B, 1y) each subunit has 4 TMDs (nAChR like)
44
where on the GABA(A) receptor (ionotropic) does GABA bind
between the a and B subunits (2 binding sites as there are 2xB and 2xa
45
which of the GABA receptors GABAA GABAB is ionotropic and which is metabotropic
GABAA ionotropic GABAB metabotropic
46
where are (metabotropic) GABA(B) receptors found
pre and post synaptically
47
what is the difference between GABA(A) and (B) inhibition?
GABA(B) is slower onset but longer lasting inhibition
48
what effect can GABA(A) antagonists have?
convulsions (epilepsy)
49
describe structure of GABA(B) receptor
GPCR fucntional receptor acts as a dimer 7TMDs
50
describe the dimer of the GABA(B) receptor
dimer exists between GABA(B)1 and GABA(B)2 GABA binds to GABA(B)1 and the G protein is associated with GABA(B)2 side of dimer
51
what G protein is GABA(B) coupled to and what effect does this have
Gi/o * a subunit inhibits adenylate cyclase * By subunits act on channels (presynaptically inhibits Ca2+ channel opnening) (post synaptically opening K channels causing hyperpolarisation)
52
where is glycine especially active and what is its function
spinal cord and brainstem → regulation of motorneurone activity also found in retina and auditory systems inhibitory
53
describe glycine synthesis
L-serine → glycine via serine hydroxymethyl transferase
54
what enzyme converts L-serine to glycine
serine hydroxymethyl transferase
55
describe reuptake of glycine
into astrocyted via Na gradient into pre and post synaptic membranes
56
what type of receptor is glycine?
ion channel | (nAChR like)
57
describe the subunit composition of the glycine receptor
5 subunits (two types, a and B) always either (2xa and 3xB) or (3xa and 2xB) each subunit has 4 TMDs
58
where is the glycine binding site
on the a subunit
59
what are the effects of glycine antagonists
convulsions (epilepsy)

physiology and pharma (18 decks)

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