Cellular Response To Action Potentials

Question 0

What triggers the release of acetylcholine?

Answer 0

An increase in intracellular calcium concentration. This is caused by an action potential which opens voltage-gated calcium channels. Calcium binds to synaptotagmin which leads to formation of the snare complex and Ach release.

Question 1

What is fast synaptic transmission?

Answer 1

The receptor protein is also an ion channel. Binding of transmitter causes the channel to open

Question 2

Name a competitive blocker

Answer 2

Tubocurarine

Question 3

How do competitive blockers work in acetyl choline channels?

Answer 3

Bind at the molecular recognition site for Ach.

Question 4

How do depolarising blockers work?

Answer 4

Cause a maintained depolarisation at the post-junctional membrane. Adjacent sodium channels are not activated because of accommodation.

Question 5

Example of a depolarising blocker and what it is used for

Answer 5

Succinylcholine

Induce paralysis

Question 6

Pathology of myasthenia gravis?

Answer 6

Antibodies directed against nicotinic Ach receptors on the postsynaptic membrane of skeletal muscle. Endplate potentials are reduced in amplitude.

Question 7

Symptoms of myasthenia gravis?

Answer 7

Drooping eyelids, profound weakness, fatigue

Question 8

How is myasthenia gravis treated?

Answer 8

Ach-esterase inhibitors which increase the amount of time Ach is in the synaptic cleft.

Question 9

Name some cellular processes which are calcium sensitive

Answer 9

Fertilisation
Secretion
Neurotransmission
Metabolism
Contraction
Apoptosis
Learning and memory 
Necrosis

Question 10

Why does selectively blocking a calcium channel often have a local effect

Answer 10

Because calcium channels have structural diversity and different calcium channels have different primary locations.

Question 11

Where are L-type calcium channels found?

Answer 11

Muscles, neurones and lungs

Question 12

What can L-type calcium channels be blocked by?

Answer 12

Dihydropyridines such as nifedipine

Question 13

What causes calcium entry into a cell to release neurotransmitter?

Answer 13

Depolarisation which opens voltage-gated calcium channels

Question 14

Structure of a calcium channel?

Answer 14

Similar to a sodium channel
One polypeptide consisting of 4 homologous repeats is what makes up the pore-forming subunit
Each repeat consists of six transmembrane spanning domains
Have structural diversity

Question 15

At rest, what are the intracellular and extracellular calcium concentrations?

Answer 15

Intra: 100nM
Extra: 1-2mM

Question 16

What does the calcium gradient across the membrane rely on?

Answer 16

Relative impermeability of plasma membrane
Ability to expel calcium across the membrane using CaATPase and Na-Ca-exchanger
Intracellular calcium stores can be rapidly and non-rapidly releasable

Question 17

Affinity and capacity of Ca-ATPase?

Answer 17

High affinity, low capacity

Question 18

How does the Ca-ATPase work?

Answer 18

When concentration of calcium increases, Ca binds to calmodulin, a trigger protein.
The complex binds to Ca-ATPase and Ca is removed from the cell.

Question 19

Affinity and capacity of Na-Ca-exchanger?

Answer 19

Low affinity and high capacity

Question 20

What is moved by the Na Ca ATPase pump?

Answer 20

3 sodium in per 1 calcium out

Question 21

What do calcium buffers do?

Answer 21

Limit calcium diffusion through ATP and Ca binding proteins.

Question 22

What does the diffusion of calcium in the cell depend on?

Answer 22

The concentration of calcium buffer proteins and the level of saturation.

Question 23

What channels increase the permeability of the membrane to calcium?

Answer 23

Voltage-gated calcium channels

Receptor-opened calcium channels

Question 24

How is calcium releases from rapidly releasable stores?

Answer 24

GPCRs
Ligand binds to GPCR on the cell membrane, activating its G-α subunit.
This binds to the membrane phospholipid, PIP2, releasing IP3.
IP3 binds to a receptor on SR, releasing calcium down its conc gradient.

Question 25

What is calcium-induced calcium release?

Answer 25

Calcium binds to ryanodine receptor on the SR/ER.

This releases calcium down its concentration gradient

Question 26

What role do mitochondria have in controlling calcium conc in cells?

Answer 26

Take it up when Ca conc is high.
Aid in buffering, regulating signalling and stimulation of ATP production.
Do it via the calcium uniporter, driven by respiration.

Question 27

What is a micro domain?

Answer 27

An area of cytoplasm with a higher than usual conc of calcium due to their proximity with the channel

Question 28

Example of the important physiological role of calcium-induced calcium release?

Answer 28

In the cardiac myocyte

• depolarisation of the membrane
• VOCCs are activated so calcium influx
• calcium bonds to the ryanodine receptor on the SR
• explosive release of calcium from intracellular stores
• calcium can bind to troponin C causing conformational shift
• tropomyosin is moved out of the binding site on the actin filament

Question 29

5 mechanisms responsible for the maintenance of the resting intracellular free calcium ion concentration?

Answer 29

Plasma membrane Ca-ATPase (PMCA)
SERCA
Na-Ca-exchange
Mitochondrial Ca uptake
Ca binding proteins

Question 30

5 mechanisms for raising intracellular free Ca concentration

Answer 30

IP3 receptors
Ryanodine receptors
Voltage-sensitive Ca channels
Na-Ca-exchange
Ligand gated Ca channels

Question 31

Which channels mediate excitation-contraction coupling in skeletal muscle contraction?

Answer 31

VOCCs

Question 32

What causes calcium release in skeletal muscle contraction?

Answer 32

Skeletal