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Undeleted > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

Give an example of a cellular role of calcium

A

Concentration changes are used to transmit information through mediation of specific bond formation.

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2
Q

How is calcium moved through a sodium/calcium exchanger

A

Generally flows out of the cell down the concentration gradient (passive, no ATP required). Calcium exchanged for sodium

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3
Q

Where is calcium ATPase located

A

Endoplasmic reticulum (ER)

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4
Q

Where does calcium in the cytoplasm go

A

Pumped out of the cell by sodium/calcium exchanger
Or
Pumped into the ER (through action of calcium ATPase) or mitochondria (down electrochemical gradient)

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5
Q

How many calcium molecules can bind to a single calmodulin molecule?

A

4

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6
Q

What happens when calcium binds to calmodulin

A

Calcium/calmodulin complex formed.
Increased affinity for target enzymes due to exposure of hydrophobic regions
Inhibition of calcium/calmodulin dependent kinase 2 is stopped. Therefore it can function.

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7
Q

Suggest methods for measuring calcium ion levels

A 
Radioactive labels
Ion-sensitive microelectrodes
Indirect electrophysiological measurements
NMR spectroscopy
Ion-sensitive dyes
Fluorescent indicators
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8
Q

What types of calcium homeostasis occur in the human body

A

Cellular - in constant oscillation
Serum - fixed
Bone - continuously changing

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9
Q

What are the calcium concentrations at rest

A

Outside ~10^-3 M
In the ER ~ 10^-3 M
Inside <10^-7 M

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10
Q

Why is calcium homeostasis important

A

The sole function of calcium is to transmit information. Requires precise concentrations to be maintained

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11
Q

Summarise the movement of calcium in a cell

A

Passive diffusion out of the stores (mitochondria/ER) into the cytoplasm
Active transport into the ER by SERCA pumps
Diffusion into the cell through voltage- and ligand-gated ion channels
Transported out of the cell by pumps and exchangers (e.g. Na/Ca exchanger)

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12
Q

How is calcium pumped out of the cytosol

A

Na/Ca exchanger on membrane (pumps Ca out, and Na in)

Ca pump in cell membrane (pumps out calcium, but requires ATP)

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13
Q

How is calcium pumped into the ER and mitochondria

A

Ca pump in ER membrane (SERCA pump; requires ATP)
Ca-binding molecules in cytoplasm
Ca import in the mitochondria

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14
Q

What are the main transporters involved in calcium transportation

A 
TRP channel (Outside calcium into cytoplasm)
PMCA (calcium pumped outside)
NCX (Na/Ca exchanger)(calcium pumped in/out of cell)
GPCR/IP3R channel (Gq receptors activated IP3 which trigger calcium release from the ER)
SERCA pump (pumps Ca into the ER)
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15
Q

Which calcium transporters are involved in keeping calcium concentrations low

A 
Na/Ca exchanger
BK channel (by blocking influx through VGCC/ROCC)
Ca-binding molecules
SERCA pump
Import into the mitochondria
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16
Q

Which calcium transporters are involved in raising calcium levels

A 
SMOCCs (GPCR)
VGCC
ROCC
IP3 pathway (GPCR + ER)(activated by RTK/insulin mGluR-S etc)
SOCCs
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17
Q

What role does Phospholipase C[beta] have with PIP3

A

Degrades to two messengers; DAG and IP3 (by catalysing hydrolysis of PIP3)

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18
Q

How does hydrolysis of PIP3 free intracellular calcium

A

Degraded to DAG and IP3
DAG activates PKC
IP3 activates IP3R channel which causes calcium efflux from the ER

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19
Q

What is the structure of IP3

A

6 carbon ring.

3 phosphate groups; 3 OH groups. Phosphate groups at 1,4,5 carbons.

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20
Q

What is the structure of the IP3 receptor (IP3R)

A

Tetramer. Each subunit has 6 TM domain. Each subunit has one IP3 binding site.
At least 3 known subtypes (S1-3) which modulate/express differently and found in different places

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21
Q

Where is the IP3R1 receptor located

A

Brain (esp cerebellum)

22
Q

What are the two key components of calcium restocking in the ER

A

Sensor (to tell when the calcium store is depleted); STIM proteins
Channel (that facilitates calcium re-entry);
ORAI proteins

23
Q

What is the role of STIM proteins

A

To detect when the ER calcium store is depleted, and activate ORAI channels

24
Q

What is the structure of ORAI proteins

A

Tetramer protein.

3 subtypes - ORAI 1-3

25
Q

What is the role of ORAI proteins

A

To facilitate calcium entry into the ER

26
Q

When does calcium accumulation by the mitochondria occur

A

Commonly seen in necrotic and apoptotic cell death. May initiate apoptosis

27
Q

How does calcium travel into the inner mitochondrial matrix

A

Outer membrane is highly permeable to calcium (lots of VDACs present).
From the outer to inner membrane calcium entry is favoured by electrochemical gradient.

28
Q

What are the main pathways for calcium to get in and out of the mitochondria

A 
Mitochondrial Calcium Uniporter (MCU)(influx)
Mitochondrial Na/Ca exchanger (mNCX)(influx and efflux)
Mitochondrial H/Ca exchanger (mHCX)(influx and efflux)
Mitochondrial PTP (mPTP)(efflux)
29
Q

What is the Mitochondrial Calcium uniporter (MCU)

A

Highly selective low conductance calcium channel. Allows calcium influx

30
Q

What is the mitochondrial Na/Ca exchanger (mNCX)

A

Isoform of the NCX on the plasma membrane. Mediates low affinity calcium exchange with sodium. (influx + efflux)

31
Q

What is the mitochondrial PTP (mPTP)

A

A channel that allows calcium efflux. Opens under pathological conditions. Also causes ATP efflux. Can activate harmful calcium-dependent proteases (e.g. calpain) to initiate cell death.

32
Q

What are MAMs

A

Mitochondrial associated matrices

They are signalling platforms where ER and mitochondrial calcium channels interact with several modulators

33
Q

How do mitochondria act as cytosolic calcium buffers

A

Buffering regulates calcium channel activity

Mitochondrial positioning controls calcium gradients

34
Q

How does mitochondria calcium buffering regulate calcium channel activity

A

Rapid removal or addition of calcium modifies the local calcium concentration in the cytosol. This can open/close the calcium channel activity (think IP3). Can speed up/slow down calcium concentration oscillation

35
Q

How does mitochondrial positioning control calcium gradients

A

Mitochondria can form a ‘belt’. They take up all the calcium, so can control the concentration that is released on the other side.
Can occur in a neuron.

36
Q

How is calcium involved with IP3R activation/inactivation

A

Calcium promotes calcium release from IP3 receptors (self amplification)
Very high calcium concentrations can inhibit the IP3R channel and terminate release

37
Q

What binding sites does the IP3R have

A

Binding site for IP3
Activating binding site for Calcium
Inhibiting binding site for calcium

38
Q

What are the affinities for calcium at the binding sites of IP3R

A

Activating site has a higher affinity
Inhibiting site has a lower affinity
(therefore inhibition takes longer)

39
Q

What are the names for the various channel opening events

A

Single - Blip
Multiple blips - Puff
Multiple puffs - Wave

40
Q

How are calcium waves propagated

A

Calcium induced calcium release from the IP3R

41
Q

What are the three main types of calcium channel

A 
Voltage dependent calcium channels (plasma membrane)
IP3-gated calcium release channels (ER membrane)
Ryanodine receptor (ER membrane)
42
Q

What are intercellular oscillations and how can they be used

A

Calcium can travel through gap junctions and signal neighbouring cells (proven with dye).
Example. Can be used in glia beta cells to synchronise calcium and release insulin.

43
Q

How does the calcium/calmodulin complex activate Ca/CaM dependent kinase 2

A

Automatically inhibited (catalytic site blocked). Autoinhibitory domain is removed by Ca/CaM. Results in autophosphorylation and activation.

44
Q

Where is Ca/CaM dependent kinase 2 mainly located

A

Neurones. Specifically in the postsynaptic density (PSD)

45
Q

Give an example of the role played by Ca/CaM dependent kinase 2

A

Plays an important role in the induction of long-term potentiation (LTP). The cellular equivalent of learning and memory.

46
Q

How can Ca/CaM dependent kinase 2 result in long term potentiation

A

When Ca/CaM is bound to the Ca/CaM dependent kinase 2, it is autophosphorylated. When Calcium and calmodulin dissociated, it remains phosphorylated (activation is prolonged).
CaMK2 can phosphorylate AMPA receptor subunits (can last ~ 30 mins), and initiate addition of new AMPA receptors

47
Q

What are the downstream events associated with the NMDA receptor

A

Calcium increased
Calcium/calmodulin complex formed, causing:
Activation of CaMK2
Calcineurin

48
Q

What is the role of calcineurin in long term depression (LTD)

A

Regulates phosphatase 1.
Inhibition of calcineurin blocks LTD
LTD results from removal of AMPA receptors (endocytosis)

49
Q

How is dye loaded into cells to test for calcium

A 
Acetoxymethyl esterconjugation (AM) for easy loading.
Free acids (charged) loaded directly via microelectrodes
50
Q

What are two methods to detect fluorescence

A

Conventional charge-coupled device (CCD)/camera based imaging
and
Confocal imaging

51
Q

Which is the dye of choice for fluorescently labelling calcium

A

Fura-2 because it can be activated at two different wavelength, allowing for internal controls.

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