M&R Session 5- Intracellular Calcium Control

Question 0

At basal calcium levels which way is the concentration gradient?

Answer 0

From out to in

Question 1

Why does calcium have to be regulated?

Answer 1

Because calcium can’t be metabolised.

Question 2

What is the advantage of a large inward calcium gradient?

Answer 2

An increase in calcium intracellularly can increase rapidly without much movement of calcium.

Question 3

Why is a large inward gradient of calcium a disadvantage?

Answer 3

Because high intracellular calcium is toxic to cells.

Question 4

What four things does a calcium gradient rely on?

Answer 4

• membrane impermeability
• calcium expulsion
• calcium buffers
• intracellular calcium stores.

Question 5

What do calcium buffers do?

Answer 5

They limit diffusion by binding to calcium. Calcium diffusion then depends upon the concentration of the binding molecule and their saturation.

Question 6

What are the two categories of intracellular calcium stores?

Answer 6

• rapidly releasable stores

- non-rapidly releasable stores

Question 7

What are the two main methods of expelling calcium across the membrane?

Answer 7

• calcium ATPase - if intracellular calcium is high, calcium binds to calmodulin and this complex binds to the ATPase and calcium is then expelled from the cell.
• NCX- transports three sodium in for one calcium to be expelled.

Question 8

What are the two ways that calcium enters the cell from outside?

Answer 8

• VOCC- is triggered by membrane depolarisation and open to allow the movement of calcium ions into the cell.
• receptor operated calcium channels- a ligand or agonist binds to the receptor, causing it to open and allow calcium to move in.

Question 9

What are the 2 ways that calcium is rapidly released from stores?

Answer 9

• G protein coupled receptors. - a ligand binds to the GPCR in the cell membrane, activating the G alpha Q subunit, which binds to PIP2, releasing IP3. IP3 binds to receptors on the SR, causing Calicut to be released.
• CICR- calcium binds to ryanodine receptors on the side of SR, stimulating further release of calcium into the cell.

Question 10

What is the non rapidly releasable method of calcium expulsion into the cell?

Answer 10

When intracellular calcium levels are high, the mitochondria take it up using a uniporter, as a protective mechanism.

Question 11

What 3 factors are required for returning calcium to basal levels?

Answer 11

• signal termination
• calcium removal
• calcium store refilling.

Question 12

How are calcium stores refilled? (2)

Answer 12

• calcium recycling

- store-operated calcium channels between mitochondria and the SR.