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ICPP * > S7 Intracellular Signalling - GPCRs > Flashcards

S7 Intracellular Signalling - GPCRs Flashcards

1
Q

What are store operated channels (SOC)?

A

Used for slow release of Ca2+ when all other sources are depleted

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2
Q

What is calmodulin?

A

An intracellular sensor of calcium ion concentration

It modulates the activity of PMCA

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3
Q

What is a G-protein made up of?

A

GDP, alpha subunit (i/s/q), gamma and beta subunits

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4
Q

What is the general order of a signal cascade?

A

Receptor (GPCR) —> Messenger associated proteins (G-protein) —> Effector (enzyme/ion channel) —> secondary messenger

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5
Q

Give examples of enzymes and their associated secondary messengers.

A

Adenylyl cyclase - cAMP

Phospholipase C - IP3 (+ DAG)

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6
Q

What is converted to produce: cAMP

IP3 (+ DAG)

A

ATP

PIP2

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7
Q

What is the process for stimulation of adenylyl cyclase?

A
  1. Agonist binds and activates the GPCR
  2. GDP for GTP exchange leads to dissociation of alpha-s subunit occurs (gamma and beta subunits also dissociate from receptor)
  3. This dissociation and exchange activates adenylyl cyclase.
  4. Adenylyl cyclase converts ATP into cAMP
  5. cAMP activates PKA (protein kinase A) which phosporylates other biological molecules
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8
Q

What are some examples of Gs-coupled receptors?

A
  1. Beta-adrenoceptors
  2. D1-dopamine receptors
  3. H2-histamine receptors
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9
Q

What is the process for inhibition of adenylyl cyclase?

A
  1. Agonist binds ad activates the GPCR
  2. GDP for GTP exchange leads to dissociation of the alpha-i subunit (and gamma and beta subunits)
  3. This dissociation inhibits adenylyl cyclase
  4. No conversion of ATP into cAMP
  5. No activation of PKA
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10
Q

What are some examples of Gi-coupled receptors?

A
  1. Alpha-2 adrenoceptors
  2. D2-dopamine receptors
  3. Mu-opioid receptors
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11
Q

What is the structure and function of PKA?

A

Has two regions - R (regulatory) subunits and C (catalytic) subunits

The cAMP (4 molecules, 2 to each subunit) binds to the R region which causes the release of the C subunits which phosphorylate target proteins in the cell

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12
Q

What is the process for stimulation of phospholipase C?

A
  1. Agonist binds and activates the GPCR
  2. GDP for GTP exchange occurs leading to dissociation of the alpha-q subunit (also dissociation of gamma and beta subunit)
  3. This dissociation activates phospholipase C (PLC)
  4. PLC converts PIP2 to IP3 and DAG
  5. The IP3 binds to IP3 receptors (ryanodine receptors) on the ER which causes release of Ca2+ from ER
  6. Increase in Ca2+ causes a CICR, Ca2+ activates PKC which binds to DAG
  7. PKC (protein kinase C) phosphorylates proteins
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13
Q

What are some examples of Gq-coupled receptors?

A
  1. Alpha-1 adrenoceptors
  2. M1-muscarinic receptors
  3. H1-histamine receptors
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14
Q

What is signal amplification?

A

The idea that a few molecules of ligand binding to the receptors causes a cascade of reactions in which many molecules are produced and activated

E.g a few adrenaline molecules binding to beta-adrenoceptors causes a relatively small cascade, but the activation of adenylyl cyclase generates MANY molecules of cAMP which activates PKA

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15
Q

How is activation of adenylyl cyclase or phospholipase C stopped?

A

GTPase breaks down GTP into GDP which means the alpha subunit no longer can activate the enzyme (effector) and the subunits join back together at the GPCR

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16
Q

Describe positive inotropy the heart.

A
  1. Adrenaline and noradrenaline can bind to ventricular beta-1 adrenoceptors
  2. Leads to activation of PKA which phosphorylates VOCC (voltage operated calcium channels) which allows more Ca2+ to enter each time
  3. More Ca2+ inside cell leads to more stimulation of muscle cells so more heart muscle contraction
17
Q

What is negative inotropy in the heart?

A

Decreased muscle contraction - could be due to drugs?

18
Q

How does sympathetic release of noradrenaline act on smooth muscle causing vasoconstriction?

A
  1. Noradrenaline binds to alpha-1 adrenoceptors
  2. Leads to production of IP3 (which releases Ca2+) and PKC activation
  3. Increased Ca2+ concentration and increase PKC activity inside cell leads to increased muscle contraction
19
Q

How does parasympathetic release of ACh lead bronchoconstriction?

A
  1. ACh binds to M3 muscarinic receptors
  2. Ultilizes Gq -phosphoplipase C-IP3/Ca2+/DAG/PKC pathways
  3. Increases smooth muscle contraction
20
Q

How are GPCRs involved in modulation of NT release? Give an example of a ligand and the receptor type in this modulation?

A

The beta-gamma subunits inhibit specific VOCCs leading to a reduction in Ca2+ influx and hence NT release.

Morphine binding to a mu-opioid G-protein associated receptor

21
Q

What are the 3 factors in GPCRs?

A
  1. Diversity
  2. Specificity
  3. Amplification
22
Q

What is signal transduction?

A

Involves intracellular signalling molecules

23
Q

What are some exogenous agonists for GPCRs?

A
  1. Salbutamol - binds to beta-2 adrenoceptors - anti-asthma drug
  2. Morphine - binds to mu-opioid receptor - anaesthetic
24
Q

What are some exogenous antagonists for GPCRs?

A
  1. Propranolol - binds to beta-adrenoceptor - treats hypertension (prevents noradrenaline from binding and increasing pressure)
  2. Sulpiride - binds to D2 dopamine receptor - neuroleptic drug
25
Q

What do sensory GPCRs sense?

A

Light (e.g. rhodopsin), odours and tastes

26
Q

What can GPCRs respond to?

A

Ions (H+, Ca2+), NTs (ACh), peptide and non-peptide hormones (glucagon and adrenaline) and large glycoproteins (TSH)

27
Q

How do GPCRs respond to agonist ligands?

A

Change their 3D shape

28
Q

What do activated GPCRs activate?

A

Intracellular proteins (G-proteins)

29
Q

Binding of ACh to M2 and M4 muscarinic receptors cause inhibition or stimulation of adenylyl cyclase?

A

Inhibition

30
Q

Binding of ACh to M1 and M3 muscarinic receptors cause inhibition or stimulation of phospholipase C?

A

Stimulation

31
Q

How does pertussis toxin (PTx) interfere with G-protein function?

A

PTx causes whooping cough so acts within respiratory tract.

PTx inhibits GDP for GTP exchange in Gi-GPCRs meaning no reactions occur past this point and no inhibition occurs

32
Q

How does cholera toxin (CTx) interfere with G-protein function?

A

CTx prevents termination of signalling by Gs-GPCRs which leads to long lasting activation of pathways (inhibits GTPase activity)

ICPP * (10 decks)

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