Session 5 - Effects Of Electrical Signals And Control Of Calcium Concentration Flashcards
What other voltage gated ion channels are calcium channels similar to?
Voltage gated sodium channels
What can be said about the variety of calcium ion channels?
There is a large amount of diversity
Will a voltage gated calcium ion channel blocker block all of the channels?
Not necessarily has because of the diversity of the channels blockers may have a localised effect
Why is synaptic transmission fast?
The receptor protein is also an ion channel
Describe the process by which calcium ion influx causes neurotransmitter release in pre-synaptic membranes.
- 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
How does the released ACh cause depolarisation?
- Binds to nicotinic ACh receptors
- causes the channel to open
- sodium enters the cell and potassium leaves
- influx of sodium causes depolarisation
What are competitive blockers?
Molecules that bind at the molecular recognition sites for ACh therefore preventing it from binding, hence preventing depolarisation
Give an example of a competitive blocker
Tubocurarine
What are depolarising blockers?
Molecules that cause a maintained depolarisation at post-junctions like membranes. This causes adjacent sodium ion channels to not be activated due to accommodation
Give an example of a depolarising blocker
Succinylcholine
What is Myasthenia Gravis?
- 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
How is Myasthenia Gravis treated?
Using Acetylcholinesterase inhibitors to increase the time ACh is in the synaptic cleft
Name some processes that are calcium sensitive
Fertilisation, secretion, neurotransmission, metabolism, contraction, learning, memory, apoptosis and necrosis
What are the approximate calcium concentrations in and outside of a cell?
Inside - 1-2mM
Outside - 100nM
What is an advantage to having a large calcium gradient across the membrane?
Changes in internal calcium concentration require very little movement of ions
What is a dis-advantage to having a large calcium gradient across the membrane?
Calcium overload can lead loss of regulation and cell death
What 4 things does the calcium gradient rely on?
1- relative impermeability of the plasma membrane
2- The ability to expel calcium
3- Calcium buffers
4- Intracellular calcium stores
What are the two main proteins that expel calcium from a cell?
Calcium-ATPase - High Affinity, Low Capacity
NCX - Low Affinity, High Capacity
How can the calcium concentration within a cell be increased?
1- Changing the membrane potential
2- Release from rapidly releasable stores
3- Release from non-rapidly releasable stores
What are the two proteins in which calcium can enter the cell via?
Voltage gated calcium channels
And
Receptor operated ion channels
Which protein helps store calcium?
SERCA - into the SR and ER
How do G-protein coupled receptors result in an increase in calcium concentration within a cell?
- 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
Which receptors does calcium bind to in CICR?
Ryanodine receptors on the SR or ER
Where is CICR particularly important physiologically?
Cardiac myocytes
Calcium enters cells Voltage gated calcium channels
Binds to ryanodine receptors
Causes explosive release of large Intracellular stores of calcium
What does the return of calcium concentrations to a basal level require?
- Termination of signal
- Caclium removal
- Calcium store refilling
Which channel allows mitochondrial calcium to replenish the SR stores?
Store-operated Calcium channels (SOCs)
What happens to calcium channels upon the arrival of an AP at a pre-synaptic membrane and what does this cause?
The voltage gated calcium channels open resulting an influx of calcium. This causes the release of neurotransmitter into the synaptic cleft
