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GPCRs/Calcium Flashcards

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1
Q

What is the normal extracellular Ca2+ concentration?

A

1x10-3 M (1mM)

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2
Q

What is the normal intracellular Ca2+ concentration?

A

1x10-7 M (100nm)

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3
Q

What is the normal SER/SR Ca2+ concentration?

A

2-3x10-4 M (200-300 micromoles)

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4
Q

What channels cause the influx of Ca2+ into the cytosol from the extracellular fluid? (4)

A

VOCC
Ligand Gated ion Channels
Store operated ion channels

NCX (when cell is heavily depolarised)

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5
Q

What channels cause the efflux of Ca2+ from the cytosol out of the cell?

A

NCX

PMCA

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6
Q

Which molecules are moved by the NCX? How many of each?

A

3Na+ into the cell

1Ca2+ out of the cell

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7
Q

What provides the concentration gradient for the movement of Na+ and Ca2+ at the NCX?

A

Concentration gradient set up by the Na/K ATPase pump

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8
Q

Which channels can result in the efflux of Ca2+ from SER/SR stores?

A 
Ryanodine Receptors (RyRs)
IP3 receptors
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9
Q

What type of GPCRs are activated to produce IP3 that can bind with IP3 receptors?

A

Galpha-q associated GPCRs

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10
Q

What acts as the ligand at RyRs? What is the process of efflux of Ca2+ at RyRs called?

A

Calcium ions

Calcium Induced Calcium Release

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11
Q

In which muscles is contraction driven by CICR?

A

Smooth muscle

Cardiac muscle

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12
Q

What is the main driver of Ca2+ release for contraction in skeletal muscle?

A

The T-tubule VOCCs are directly coupled with RyRs, so when VOCCs open, RyRs open

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13
Q

What proteins act to regulate Ca2+ cytosol concentrations and slows down diffusion of the ions within the cytoplasm?

A

Calcium ion buffer proteins

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14
Q

What is an example of a Ca2+ binding protein? Give an example of a protein it interacts with? How many calciums can it bind?

A

Calmodulin
Regulates activity of PMCA
Binds up to 4 calcium ions

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15
Q

What are the 3 superfamilies of cell surface receptor?

A

Kinase linked receptors (receptors with intrinsic enzymatic activity)

Ligand Gated ion Channels

G protein coupled receptors

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16
Q

Give an example of a ligand Gated ion channel. Give an example of a kinase linked receptor. Give an example of a GPCR.

A

Nicotinic ACh receptor

Insulin receptor

Muscarinic ACh receptor

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17
Q

What is affinity?

A

How well a ligand binds

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18
Q

What is efficacy?

A

How well a ligand causes a response

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19
Q

What is an agonist?

A

Molecule that binds to a receptor and activates it

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20
Q

What is an antagonist?

A

Molecule that binds to a receptor and does not activate it

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21
Q

Give two examples of B2-adrenoceptor agonists? Which disease are these drugs used in the treatment of?

A

Salbutamol
Salmeterol

Asthma

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22
Q

Give two examples of u-opioid receptor agonists? What are they used for?

A

Morphine, fentanyl

Analgesia/anaesthesia

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23
Q

Give two examples of b-adrenoceptor antagonists. What are they often used to treat?

A

Propranolol
Atenolol

Hypertension

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24
Q

Give two examples of d2-dopamine receptor antagonists. What are they used to treat?

A

Haloperidol
Sulpiride

Schizophrenia

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25
GPCRs can respond to a small variety or great variety of stimuli?
A great variety of stimuli
26
GPCRs consist of how many polypeptide chains?
1
27
Why are GPCRs sometimes called 7TM receptors?
They have 7 transmembrane spanning regions
28
What is the position of the n terminal and c terminal at GPCRs?
Extracellular n terminal Intracellular c terminal
29
What two places at GPCRs do ligands typically bind?
At a ligand binding site buried between the TM domains (made up by 2-3 of the domains) At the n terminal region
30
What are two examples of ligands that bind between the TM domains at GPCRs?
Adrenaline | Acetylcholine
31
What are two examples of ligands that bind to GPCRs at the n terminal?
Glutamate | Thyroid stimulating hormone
32
What does binding of a ligand do to a GPCR?
Causes a conformational change in the GPCR - activating it and allowing it to interact with G proteins
33
What subunits make up a G protein?
Alpha Beta & Gamma (Function together) Make up a heterotrimer
34
What does interaction of the activated GPCR with the G protein result in?
GDP ----> GTP on the alpha subunit of the G protein Immediate dissociation of the alpha subunit from the beta/gamma subunit
35
Why is GTP able to bind readily to the alpha sub unit once it is activated to?
GTP is present at high concentrations in the cell
36
What happens to the two separated units of the G protein to cause a response?
They each interact with effector proteins
37
Where in the cell do all the steps of G protein activation, termination etc occur?
On the plasma membrane
38
How is G protein signalling terminated?
GTP is hydrolysed to GDP The alpha sub unit possesses GTPase activity and hydrolyses the GTP High affinity between the two subunits returns, inactive G protein reformed
39
Which G proteins are all beta-adrenoceptors associated with? What is the enzymatic result of their activation?
G-alpha-S Increased adeneylyl cyclase
40
What G proteins are the m4 muscarinic ACh receptors associated with? What is the enzymatic result of their activation?
G-alpha-i Decreased adenylyl cyclase
41
On which GPCRs does pertussis toxin have its effect?
Gi GPCRs
42
What effect does Pertussis toxin have on the Gi protein?
Causes covalent modification No GDP/GTP exchange G proteins can't be activated
43
What G proteins are affected by cholera toxin?
Gs proteins
44
What effect does cholera toxin have on the G protein?
Makes the G protein unable to hydrolyse GTP Permanently activated G protein
45
Which reaction does adenylyl cyclase catalyse?
ATP ----> Cyclic AMP
46
Which reaction does phospholipase C catalyse?
PIP2----> IP3 + DAG
47
What reaction does PI3K catalyse?
PIP2----> PIP3
48
What reaction does cGMP phosphodiesterase catalyse?
Cyclic GMP ---> 5'-GMP
49
What are examples of effectors at the ends of GPCR pathways?
Enzymes Ion channels VOCCs
50
Why is the cell not deprived of ATP during increased activity of adenylyl cyclase?
In reality it is a relatively small side reaction
51
What does cyclic AMP primarily bind to after it has been produced?
PKA
52
Name 2 GPCRs other than b-adrenoceptors that are Gs preferring.
D1-dopamine receptors | H2-histamine receptors
53
Name two examples of Gi preferring GPCRs other than a2, m2 and m4 receptors.
D2-dopamine receptors | u-opioid receptors
54
What is the structure of PKA?
Has 4 sub units 2 Regulatory 2 catalytic
55
How does cyclic AMP interact with PKA?
Cyclic AMP binds with the regulatory sub units of PKA Release of catalytic sub units
56
What does PKA do?
Phosphorylate different substrates
57
Other than the pumps that exist, how else is the very low intracellular calcium ions concentration maintained?
Relative impermeability of the plasma membrane and calcium binding proteins
58
Which GPCRs result in increased phospholipase C activation?
Gq preferring GPCRs
59
What substrate does phospholipase C work on?
PIP2 Cleaves it to form IP3 and DAG
60
What does increased DAG production result in?
Activation of PKC
61
The activation of IP3 receptors can increase intracellular calcium ion concentration how many fold within a few seconds?
5-10 fold
62
Other than a1, m1 and m3 receptors, name a receptor that prefers Gq proteins?
H1-histamine receptors
63
Increased intropy is the result of activation of which receptors? How does it cause increased force of contraction?
B1-adrenoreceptors PKA phosphorylates VOCCs, increased calcium ---> increased contraction
64
Vascular smooth muscle contraction (vasoconstriction) is controlled by which GPCR?
a1-adrenoceptors
65
Bronchoconstriction can be affected by which GPCR?
M3-muscarinic receptors
66
What is an example of an effector molecule for the activated beta/gamma subunit?
VOCCs
67
What effect can beta/gamma sub units have at VOCCs at synapses?
Inhibit specific VOCCs reducing calcium influx, reducing neurotransmitter release

ICPP (8 decks)

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