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PMCOL 371 > 8 - Ligand-gated > Flashcards

8 - Ligand-gated Flashcards

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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 (18 decks)

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