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PMCOL 371 - Cellular Neuroscience > 8 - Ligand-gated > Flashcards

8 - Ligand-gated Flashcards

1
Q

Ligand-gated ion channel receptors (LGICs) mediate _______ responses

A

Ligand-gated ion channel receptors (LGICs) mediate fast synaptic responses

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2
Q

Some LGICs are ______-selective while others are ______-selective

A

Some LGICs are Anion-selective while others are Cation-selective

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3
Q

In LGIC’s the receptor and channel are:

A

a part of the same receptor complex

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4
Q

LGIC receptors are ______, ______ proteins

A

LGIC receptors are large, multisubunit proteins (oligomers)

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5
Q

What are three examples of LGICs

A
  • Peripheral nAChR (nicotinic receptors)
  • GABAA receptor
  • Glutamate receptors
    • NMDA, AMPA, Kainate
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6
Q

Function of LGICs

A
  • Mediate fast synaptic responses
  • Essential for rapid communication within nervous system
  • Activation can happen in submillisecond timescale
  • Always an increase in membrane conductance
  • Ions flow down their concentration gradient
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7
Q

Receptors _______ in continued presence of agonist

A

Receptors desensitize in continued presence of agonist

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8
Q

Transmitter action is ended with ______, _______ and/or ______ of transmitter

A

Transmitter action is ended with destruction, diffusion and/or reuptake of transmitter

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9
Q

Two reasons why nicotinic acetylcholine receptors (nAChR) are so well studied:

A
  • Abundant in the electric organs of the torpedo fish
  • Availability of a high affinity probe: the snake toxin alphabungarotoxin
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10
Q

The peripheral nAChR is a ______ of four _______ subunits

A

The peripheral nAChR is a pentamer of four homologous subunits (alpha2beta-gamma-delta)

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11
Q

The peripheral nAChR has ____ alpha subunits with a total of ___ subunits

A

The peripheral nAChR has 2 alpha subunits with a total of 5 subunits

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12
Q

Subunits of the peripheral nAChR form a ______ complex around the central ion ____

A

Subunits of the peripheral nAChR form a pseudosymmetric complex around the central ion pore

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13
Q

Functional properties of nAChR

Release of ACh leads to binding to the _____ which has what effect on the channel

A

Functional properties of nAChR

Release of ACh leads to binding to the nAChR which opens the nAChR within about 0.3msec

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14
Q

The nAChR is much more likely to open if what happens?

A

Positive Cooperativity: ACh molecules bind to each of the two binding sites

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15
Q

The nAChR channel is ______-selective with a diameter of _____

A

The nAChR channel is cation-selective with a diameter of 0.65nm

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16
Q

Synaptic transmission is normally terminated by the action of _______

A

Synaptic transmission is normally terminated by the action of acetylcholinesterase (AChE)

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17
Q

What happens to the nAChR in the continued presense of ACh?

A

The receptor becomes desensitized

Channel closes and the receptor adopts a conformation with a high affinity for ACh

Agonist must unbind and the receptor must rest to return to activatable conformation

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18
Q

What is the difference between muscle nAChRs in adults and embryos?

Subunits?

Conductance?

Burst duration?

A
  • Adult junctional receptor
    • alpha2-beta-epsilon-delta subunits
    • Large conductance (60ps)
    • Short burst duration
  • Embryonic and denervated
    • alpha2-beta-gamma-delta subunits
    • lower conductance (40ps)
    • Longer burst duration
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19
Q

Neuronal nAChRs

  • subunits
  • blocked by:
A
  • stoichiometry alphanbetam
  • blocked by k-bungarotoxin
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20
Q

How are chimeric receptors constructed?

A

By inserting the amino acid sequence of one receptor into the corresponding region of another

OR

by substituting subunits from other organisms (eg mouse vs torpedo)

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21
Q

What is possible if we characterise the properties of the chimera receptor?

A

By characterising the properties of the chimera it is possible to explore the functional importance of different parts of the protein or (as here) oligomer

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22
Q

___ subunits are important in conferring nAChR channel properties

A

delta subunits are important in conferring channel properties

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23
Q

Which receptor is the major inhibitory LGIC in the CNS?

A

GABAA

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24
Q

GABA causes __________ potential

A

fast inhibitory postsynaptic potential (IPSP)

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25
What are two GABAA agonists?
GABA, muscimol
26
What is one antagonist to the GABAA receptor
Bicuculline
27
\_\_\_\_\_ is a GABAa channel blocker
Picrotoxin (also blocks glycine receptor chlorine channel)
28
Receptor binding similarity between GABAA and nAChR?
Both show positive cooperativity to agonist
29
Which drugs have binding sites on the GABAA receptor?
* Benzodiazepines * Tranquilizers, hypnotics, anxiolytic, antipanic and anticonvulsants * Barbiturates * Steroids
30
Effect of benzos on GABAA What does it require?
* Increase affinity of GABAA for GABA * Increase frequency of channel opening * Potentiates GABA actions * Requires GABA agonist for its actions to be seen
31
Effect of barbiturates on GABAA
* Potentiate actions of GABA by shifting the dose-response curve to the left and increasing the maximum response * Increase channel open lifetime
32
Effect of steroids on GABAA
* Potentiate actions of GABA * Increase channel opening frequency and open lifetime
33
Pentobarbital greatly increases both: (of GABAA)
Opening probability Single channel conductance
34
\_\_\_\_\_\_\_\_ can open channel in the absence of GABA
_barbiturates_ can open channel in the absence of GABA (unlike benzos)
35
\_\_\_\_\_\_ interface has binding site for GABA
beta-alpha interface has binding site for _GABA_
36
Benzodiazepine binding site at ______ interface
Benzodiazepine binding site at _alpha-beta_ interface
37
Which subunit is necessary for expression of benzodiazepine binding site?
Gamma subunit
38
Commonly, GABAA receptors in the brain consist of which subunits?
two alpha two beta one gamma
39
\_\_\_\_\_\_ is the major excitatory transmitter in the brain
_glutamate_ is the major excitatory transmitter in the brain
40
Glutamate receptors are _______ channels
Glutamate receptors are \_\_\_**_Cation_**\_\_\_ channels (Na+ K+ Ca++)
41
Glutamate receptor subtypes are defined by:
Specific agonists: NMDA (activated by N-methyl-D-Aspartate) non-NMDA (AMPA and Kainate receptors)
42
Glutamate receptors mediate _______ excitation
Glutamate receptors mediate _fast synaptic_ excitation
43
Glutamate receptors are involved in _________ (important in learning and memory)
Glutamate receptors are involved in _SYNAPTIC plasticity_ (important in learning and memory)
44
What is synaptic plasticity?
Long-lasting, activity dependent changes in synaptic efficacy
45
Excess glutamate transmission is involved in \_\_\_\_\_\_\_
Excess glutamate transmission is involved in _neuronal cell death (excitotoxicity)_
46
When is excitotoxicity observed?
Following hypoxia, hypoglycemia, ischemia, epilepsy
47
Excitotoxicity may be due to ______ influx through NMDA and non-NMDA receptors (glutamate receptors)
Excitotoxicity may be due to _Ca++_ influx through NMDA and non-NMDA receptors (glutamate receptors)
48
Functions of AMPA receptors
AMPA receptors are a subtype of glutamate receptor * fast synaptic transmission * targets for memory-enhancing drugs
49
Functions of Kainate receptors
Subtype of glutamate receptor * fast synaptic transmission * some presynaptic potentiating actions
50
Functions of NMDA receptors?
subtype of glutamate receptor * Ca++ influx * trophic developmental actions * learning and memory * excitotoxicity * Slower than non-NMDA receptors
51
Glutamate receptors have _____ transmembrane domains
Glutamate receptors have _3_ transmembrane domains Q/R site at M2
52
GluR1-GluR4 * high affinity for \_\_\_\_\_\_ * form ______ channels * gated by _____ and \_\_\_\_\_\_ * preferentially conduct \_\_\_\_, some conduct \_\_\_\_\_ * Any channel containing _____ is Ca++ impermeable * Blocked by \_\_\_\_\_, \_\_\_\_\_, _____ and \_\_\_\_\_\_
GluR1-GluR4 * high affinity for _AMPA receptors_ * form _homomeric_ channels * gated by _AMPA_ and _Kainate (and glutamate)_ * preferentially conduct _Na+_, some conduct _Ca++_ * Any channel containing _GluR2_ is Ca++ impermeable * Blocked by _CNQX, NBQX (AMPA and kainate), GYKI53655 (AMPA-selective)_ and _kynurenic acid (non-selective glutamate)_
53
GluR5-GluR7 High affinity for \_\_\_\_\_\_\_ GluR5,6 form ________ channels GluR7 does not form _______ channel
GluR5-GluR7 High affinity for _kainate receptors_ GluR5,6 form _kainate-activated_ channels GluR7 does not form _homomeric_ channel
54
KA1 and KA2 have high affinity for \_\_\_\_\_\_\_
KA1 and KA2 have high affinity for _KA binding proteins_
55
AMPA receptors: * desensitize when activated by \_\_\_\_\_\_ * Dont desensitize when activated by \_\_\_\_
AMPA receptors: * desensitize when activated by _Glu or AMPA_ * Flip has small steady-state component * Flop desensitizes fully * Dont desensitize when activated by _kainate_
56
KA receptors: * desensitize to ____ or \_\_\_\_\_ * Homomeric don't respond to \_\_\_\_\_\_ * GluR6/KA1 heteromer responds, doesn't desensitize to \_\_\_\_\_, desensitizes to \_\_\_\_\_
KA receptors: * desensitize to _Glu_ or _Kainate_ * Homomeric don't respond to _AMPA_ * GluR6/KA1 heteromer responds, doesn't desensitize to _AMPA_, desensitizes to _Kainate_
57
What are the three main classes of subunits for NMDA receptors?
* NR1 * NR2A-NR2D * NR3A&B
58
NR1 subunits of NMDA receptors form _____ channels
NR1 subunits of NMDA receptors form _homomeric_ channels
59
NR2A-NR2D subunits of NMDA receptors form \_\_\_\_\_\_channels with \_\_\_\_\_\_
NR2A-NR2D subunits of NMDA receptors form _heteromeric_ channels with _NR1_ Do NOT form channels on their own
60
NR2 subunit isoform regulates ________ (NMDA receptors)
NR2 subunit isoform regulates _channel properties_ (NMDA receptors)
61
Which subunits of NMDA receptors have the glycine binding site?
NR3A&B
62
Homomeric NR1 NMDA receptors are \_\_\_\_\_\_gated currents
Glu
63
Heteromeric (NR1 & NR2 (or NR3)) NMDA receptors * Require ___ as co-agonist * \_\_\_\_-competitive antagonist * _______ channel blockers (noncompetitive) * High ____ permeability *
Heteromeric (NR1 & NR2 (or NR3)) NMDA receptors * Require _glycine_ as co-agonist * _APV_-competitive antagonist * channel blockers (noncompetitive) * High _Ca++_ permeability * Different NR2 subunits confer different properties * kinetic * voltage dependent Mg++ block
64
Which NMDA subunit family is expressed throughout the brain
NR1
65
NMDA receptors have a _______ current-voltage relationship that is \_\_\_\_-dependent
NMDA receptors have a _non-linear_ current-voltage relationship that is _Mg2+_-dependent
66
Why don't NMDA receptors conduct well at negative potentials?
Mg2+ blocks the channel, even when opened by glutamate
67
When does Mg2+ unblock the NMDA receptor pore?
When cell is More Depolarized

PMCOL 371 - Cellular Neuroscience (19 decks)

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