Calcium

Question 1

What effect does the big difference in intracellular and extracellular concentrations in calcium have?

Answer 1

It means that very small changes in concentration have large effects inside the cell

Question 2

Why are there very low calcium levels inside the cell?

Answer 2

High calcium levels are toxic to the cell and result in cell death. It causes ossification of tissue as it calcifies the cells.

Question 3

What is the extracellular concentration of calcium?

Answer 3

1mM

Question 4

What are the 6 methods of moving calcium into the intracellular space?

Answer 4

1. Store Operated Channels (SOC)
2. Voltage Gated Calcium Ion Channels (VGCC)
3. Ligand Gated Ion Channels (LGIC)
4. Sodium Calcium Exchanger (NCX)
5. GPCR in plasma membrane
6. Ryanodine Receptors

Question 5

What are the 3 methods of moving calcium out of the cytosol?

Answer 5

1. PMCA
2. NCX
3. SERCA

Question 6

How does the sodium calcium exchange work?

Answer 6

The pump utilises the electrochemical gradient set up by the Na/K ATPase which provides a large conc of Na outside the cell. Therefore the cell moves 3 sodium ions in and 1 calcium Ion out. The pump has a low affinity for calcium

Question 7

How does the Plasma Membrane Calcium ATPase work?

Answer 7

Using one molecule of ATP to transfer one ion of calcium out of the cell. This has a high affinity for calcium and a low capacity

Question 8

How do Store Operated Channels work?

Answer 8

A sensing protein in the ER detects when calcium levels inside the cell are low and activated the Channels to open.

Question 9

How do voltage Gated Calcium Channels work?

Answer 9

The Channels open in response to depolarisation

Question 10

How to ligand Gated Ion Channels work?

Answer 10

Open when ligands bind to them, as they cause a conformational change

Question 11

How is the NCX able to transport calcium both into and out of the cell?

Answer 11

When the cell is depolarised the Exchanger can change direction to pump calcium in and sodium out to try and counteract the depolarisation as it has a net change in charge as it attempts to repolarise the cell

Question 12

How does the SERCA work?

Answer 12

Works the same as the PMCA but on the SER/ER membrane. It uses 1 molecule of ATP to transport calcium into the ER from the cytosol.

Question 13

How do GPCR receptor increase intracellular calcium levels?

Answer 13

Activation of the GPCR by an agonist causes the production of IP3 which binds to the IP3 receptor on the ER membrane (therefore acting as a LGIC) which then open allowing calcium ions to move out.

Question 14

How do Ryanodine receptors work?

Answer 14

After depolarisation VGCCs open and the calcium ions that move into the cytosol bind to the RyR receptors opening them, allowing the release of calcium ions from the ER (POSITIVE FEEDBACK)

Question 15

What is the name given to the type of CALCIUM RELEASE by the Ryanodine receptors?

Answer 15

CALCIUM INDUCED CALCIUM RELEASE

Question 16

How does CALCIUM RELEASE from SER in skeletal muscle differ from cardiac and smooth muscle?

Answer 16

In skeletal muscle the VGCCs are directly coupled to the RyR receptor and so when the VGCC open the RyR receptor also opens. Whereas in cardiac and smooth muscle the RyR must wait for a calcium Ion to bind to be activated

Question 17

What happens to the calcium Ion concentrations during exercise?

Answer 17

After exercise the intracellular CALCIUM ion concentration INCREASES

Question 18

How do CALCIUM buffers work?

Answer 18

They bind to CALCIUM ions which means the ions are no longer free. Only free calcium ions affect the concentrations. If calcium levels then fall the buffers can RELEASE the calcium to increase the concentration in the cytosol.

Question 19

How does Calmodulin (CaM) work?

Answer 19

When calcium binds CaM binds to 4 calcium ions which induce a conformational change in CaM, enabling CaM to interact with a range of proteins, e.g. PMCA transporters. This is important because some of these proteins can’t bind directly with calcium.

Question 20

What does CaM work as?

Answer 20

A calcium Sensor and Trigger protein

Question 21

What type of transports are PMCA and SERCA?

Answer 21

Primary Acrive transporters and they are directly using ATP

Question 22

What type of transport is the NCX?

Answer 22

Secondary Active transporters as it requires the electrochemical sodium gradient set up by the Na/K ATPase which requires ATP.

Question 23

What affect does Ischaemia have on The NCX?

Answer 23

The lack of blood supply means there’s less oxygen so less ATP is produced. Therefore, the Na/K ATPase is inhibited so Na accumulates inside the cell. The depolarisation of the cell reverses the NCX so it pumps sodium out and calcium in. The increase in calcium levels is then toxic for the cell.