Session 5 - Effects Of Electrical Signals And Control Of Calcium Concentration

Question 1

What other voltage gated ion channels are calcium channels similar to?

Answer 1

Voltage gated sodium channels

Question 2

What can be said about the variety of calcium ion channels?

Answer 2

There is a large amount of diversity

Question 3

Will a voltage gated calcium ion channel blocker block all of the channels?

Answer 3

Not necessarily has because of the diversity of the channels blockers may have a localised effect

Question 4

Why is synaptic transmission fast?

Answer 4

The receptor protein is also an ion channel

Question 5

Describe the process by which calcium ion influx causes neurotransmitter release in pre-synaptic membranes.

Answer 5

• Calcium ion channels open and there is a large influx
• The calcium then binds to synaptotagmin
• This causes the snare complex to form a fusion pore
• This allows the vesicle to release the neurotransmitter into the synaptic cleft

Question 6

How does the released ACh cause depolarisation?

Answer 6

• Binds to nicotinic ACh receptors
• causes the channel to open
• sodium enters the cell and potassium leaves
• influx of sodium causes depolarisation

Question 7

What are competitive blockers?

Answer 7

Molecules that bind at the molecular recognition sites for ACh therefore preventing it from binding, hence preventing depolarisation

Question 8

Give an example of a competitive blocker

Answer 8

Tubocurarine

Question 9

What are depolarising blockers?

Answer 9

Molecules that cause a maintained depolarisation at post-junctions like membranes. This causes adjacent sodium ion channels to not be activated due to accommodation

Question 10

Give an example of a depolarising blocker

Answer 10

Succinylcholine

Question 11

What is Myasthenia Gravis?

Answer 11

• autoimmune disease where antibodies target nicotinic ACh receptors on the Postsynaptic membrane of muscles
• patients have droopy eyelids and have profound weakness that increases with exercise
• Endplate potentials have decreased amplitude ->muscle weakness and fatigue

Question 12

How is Myasthenia Gravis treated?

Answer 12

Using Acetylcholinesterase inhibitors to increase the time ACh is in the synaptic cleft

Question 13

Name some processes that are calcium sensitive

Answer 13

Fertilisation, secretion, neurotransmission, metabolism, contraction, learning, memory, apoptosis and necrosis

Question 14

What are the approximate calcium concentrations in and outside of a cell?

Answer 14

Inside - 1-2mM

Outside - 100nM

Question 15

What is an advantage to having a large calcium gradient across the membrane?

Answer 15

Changes in internal calcium concentration require very little movement of ions

Question 16

What is a dis-advantage to having a large calcium gradient across the membrane?

Answer 16

Calcium overload can lead loss of regulation and cell death

Question 17

What 4 things does the calcium gradient rely on?

Answer 17

1- relative impermeability of the plasma membrane
2- The ability to expel calcium
3- Calcium buffers
4- Intracellular calcium stores

Question 18

What are the two main proteins that expel calcium from a cell?

Answer 18

Calcium-ATPase - High Affinity, Low Capacity

NCX - Low Affinity, High Capacity

Question 19

How can the calcium concentration within a cell be increased?

Answer 19

1- Changing the membrane potential

2- Release from rapidly releasable stores

3- Release from non-rapidly releasable stores

Question 20

What are the two proteins in which calcium can enter the cell via?

Answer 20

Voltage gated calcium channels
And
Receptor operated ion channels

Question 21

Which protein helps store calcium?

Answer 21

SERCA - into the SR and ER

Question 22

How do G-protein coupled receptors result in an increase in calcium concentration within a cell?

Answer 22

• Ligands binds to GPCR
• activates G alpha q sub unit
• this binds to PiP2 releasing IP3
• IP3 binds to its receptor on the SR
• Calcium released

Question 23

Which receptors does calcium bind to in CICR?

Answer 23

Ryanodine receptors on the SR or ER

Question 24

Where is CICR particularly important physiologically?

Answer 24

Cardiac myocytes
Calcium enters cells Voltage gated calcium channels
Binds to ryanodine receptors
Causes explosive release of large Intracellular stores of calcium

Question 25

What does the return of calcium concentrations to a basal level require?

Answer 25

• Termination of signal
• Caclium removal
• Calcium store refilling

Question 26

Which channel allows mitochondrial calcium to replenish the SR stores?

Answer 26

Store-operated Calcium channels (SOCs)

Question 27

What happens to calcium channels upon the arrival of an AP at a pre-synaptic membrane and what does this cause?

Answer 27

The voltage gated calcium channels open resulting an influx of calcium. This causes the release of neurotransmitter into the synaptic cleft