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3rd Year Biomed > Neuroscience - Neurotransmitter receptors > Flashcards

Neuroscience - Neurotransmitter receptors Flashcards

1
Q

What are the 2 main classes of neurotransmitter receptors?

A
  • Ionotropic receptors

- G-protein coupled (metabotropic) receptors

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2
Q

What does transmitter binding cause in both ionotropic and G-protein coupled receptors?

A

Ionotropic - binding opens an ion channel

G-protein coupled - binding activates a G-protein which, in turn, activates an effector e.g. enzyme, ion channel

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3
Q

What are the 2 main types of ionotropic receptors?

A
  • cys-loop receptors

- p-loop receptors

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4
Q

Cys-loop receptors are the receptors for what transmitters?

A
  • Nicotinic ACH
  • GABAa
  • Glycine
  • Serotonin 5-HT3 subclass
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5
Q

P-loop receptors are the receptors for what transmitter?

A

Glutamate (iGluR)

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6
Q

What are the main 2 types of G-protein coupled receptor?

A

Class A and C

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7
Q

Class A receptors are the receptors for what transmitters?

A 
Muscarinic ACH
Dopamine
Serotonin 5-HT1-2,4-7 subclasses
alpha and beta adrenergic
Most neuropeptides
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8
Q

Class C receptors are the receptors for what transmitters?

A

Glutamate (mGluR)

GABAb

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9
Q

How was nACHR first isolated?

A

Isolated from the electric organ of electric fish

- dense arrays of nACHRs

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10
Q

What is the subunit organisation of the nACHR?

A
  • Individual subunits designated alpha, beta, gamma, delta and epsilon
  • Each individual subunit has 4 transmembrane (TM) domains and extracellular N- and C- termini
  • 5 subunits assemble a pentameric structure
  • TM2 from each subunit lines the pore of the ion channel
  • 2 alpha subunits, which bind ligand, are required for a functional receptor
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11
Q

How many individual subunits are there in total? How many of each? (e.g how many alpha, beta etc)

A 
17 subunits in total
10 alpha
4 beta
1 gamma
1 delta
1 e
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12
Q

Different combinations of subunits cause what?

A

Different pentameric receptors with different conductance properties

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13
Q

Give an example of how different subunits can cause different conductance?

A

Receptors composed of alpha and beta subunits more permeable to Ca2+

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14
Q

What structural feature of the nACHR facilitates cation permeability?

A

The pore is surrounded by rings of negatively-charged amino acids

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15
Q

Per receptor, there are always 2 subunits of what type?

A

alpha

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16
Q

Where does the ligand bind to on the nACHR?

A
  • Binds to the N-terminal extracellular domain of alpha subunit and adjacent adjacent subunit (varies depending on receptor type)
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17
Q

What is the positive and negative face of the nACHR and what does each determine?

A

Positive - alpha-subunit side - determines ligand affinity

Negative - adjacent subunit - determines ligand selectivity

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18
Q

What distinguishes the alpha subunit from a non-alpha subunit?

A

2 neighbouring cysteine residues distinguish alpha from non-alpha subunits

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19
Q

What amino acids are important for binding on the negative face?

A

Leucine, methionine and tryptophan

20
Q

What facilitates nACHR channel opening/closing

A
  • Rotation of TM2 domains of each of the 5 receptor subunits closes or opens a ring of leucine and valine residues to regulate ion movement
21
Q

What amino acids line the channel to facilitate ion permeability?

A

Serine and threonine

22
Q

What are the 3 groups of ionotropic glutamate receptors (iGluR)?

A

1) NMDA
2) AMPA
3) Kainate

23
Q

What family of ionotropic receptors are iGluRs part of?

A

pore-loop channels
(p-loop channels)
includes the voltage gated K+ and Na+ ion channels

24
Q

What is the subunit organisation of the iGluR?

A
  • Each subunit has 3 TM domains and one re-entrant hairpin loop
  • Hairpin loop forms the pore of the receptor chennel
  • Extracellular domains including N-terminus and TM2-TM3 loop are very large
  • C-terminus is intracellular
  • Receptor is a tetramer of 4 subunits
25
Q

What is the overall structure of the iGluR?

A

From extracellular to transmembrane:

  • Amino terminal domain
  • Ligand binding domain
  • Transmembrane domain
  • LBD consists of 2 lobes formed from regions of N-terminus and extracellular loop between TM2 and TM3
  • P-loop forms the ion channel
26
Q

Binding of the agonist to the LBD causes what?

A

Induces a conformational change in LBD that pulls the ion channel open

27
Q

What is the unique property of NMDA receptors vs non-NMDA receptors?

A

They are Ca2+ permeable, whereas non-NMDA receptors are permeable primarily to Na+ and K+

28
Q

What are NMDAs 2 binding sites?

A

1) Mg2+ in the channel

2) Glycine acts as a cofactor required for channel opening

29
Q

At resting potential, what blocks the channel of NMDA receptors?

A

Mg2+

30
Q

What must occur to remove the Mg2+ black?

A
  • Transmitter binding followed by membrane depolarisation
31
Q

How many G-protein coupled receptor (GPCR) genes are there in the human genome?

A

Over 800

32
Q

What is the largest class of GPCRs? How many genes

A

Class A
>600 genes
Includes most GPCRs for classical and peptide neurotansmitters

33
Q

How many genes are there for Class C GPCRs and what are they receptors for?

A

20 genes

glutamate and GABAb

34
Q

What is the structure of the beta-adrenergic receptor?

A
  • Ligand binding protein is single polypeptide
  • 7 TM domains interconnected by 3 extracellular loops and 3 intracellular loops
  • N terminus extracellular
  • C terminus intracellular
  • G protein coupled to adenylate cyclase
  • receptor binding leads to production of cAMP
35
Q

How does the neurotransmitter bind in beta-adrenergic and muscarinic ACH receptors?

A
  • Transmitter binds to a pocket below the membrane, withing the hydrophobic core
  • Disulphide bond between e1 and e2 stabilses the binding pocket
36
Q

What is the structure of G proteins?

A

Heterodimeric: composed of alpha, beta and gamma subunits

37
Q

Describe the G protein binding cycle

A

Cycles between GDP and GTP bound states

1) alpha-beta-gamma G protein bound to GDP in an inactive state
2) GPCR interacts with this protein - reduced affinity for alpha subunit
3) GDP exhanged for GDP, Galpha dissociates from Gbeta-gamma
4) G protein has GTPase function, hydrolysis of GTP back to GDP

Ga-GTP and Gby are functional and can interact with effectors (adenylate cyclase)

38
Q

What activates the Type 1 neuron specific adenylate cyclase?

A

Activated by Ca2+-calmodulin binding

39
Q

What is the structure of type 1 adenylate cyclase?

A
  • Active enzyme is a tandem repeat of 6 TM domain proteins

- HAs a cytoplasmic catalytic domain that converts ATP to cAMP

40
Q

What is the primary target of cAMP?

A

Protein kinase A - serine/threonine kinase that phosphorylates many targets

41
Q

What are the 2 pathways that can activate adenylate cyclase?

A
  • Act through different G proteins: Gs and Gq
  • Gs activates Gs-alpha
  • Gq activates Ca2+-calmodulin
  • Both lead to adenylate cyclase activation (AC behaves as a coincidence factor)
42
Q

What is coincidence detection important for?

A

Associating events e.g in associative learning such as Pavlovian conditioning

43
Q

In noradrenaline signalling, state the 1st messanger, receptor, G protein transducer, effector, 2nd messanger, mediator and cellular response

A

1st messanger - noradrenaline

Receptor - B-adrenergic GPCR

G protein transducer - Gs

Effector - Adenylate cyclase

2nd messanger - cAMP

Mediator - Protein kinase A

Cellular response - regulation of ion channels/enzymes, remoddeling of cytoskeleton, changes in gene expression

44
Q

Where are pre-synaptic receptors found? What type can they be? What is their role?

A
  • Located on pre-synaptic terminals
  • May be ionotrpic or G-protein coupled
  • Modulate synaptic activity by altering transmitter release
45
Q

Give an example of how a neurotransmitter regulates the release of a seperate transmitter by pre-synaptic receptor activation?

A
  • Release of dopamine from dopaminergic neurons
  • Release modulated by ACH from a neighbouring neuron binding to presynaptic nACHR on terminals of dopaminergic neuron
  • Activation of presynaptic nACHR leads to increased presynaptic Ca2+ which enhances dopamine exoxcytosis
46
Q

What are the main 2 types of receptor regulation?

A

1) Desensitisation - reduces responsiveness of receptor to transmitter
2) Sensitisation - increases response of receptor to transmitter

47
Q

What are the 2 types of desensitisation and what causes each?

A

1) Rapid (milliseconds to minutes)
- Due to conformational changed associated with phosphorylation of receptor subunits

2) Slow (minutes to hours)
- due to removal of receptors by endocytosis
- may be reversible or irreversible

3rd Year Biomed (44 decks)

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