Regulation Of Cellular Calcium

Question 1

What are the disadvantages of a large inward gradient of calcium?

Answer 1

Energy expensive and inability to deal with calcium can lead to a calium overload which can lead to loss of regulation and cell death.

Question 2

What are the 3 overarching mecahanisms for maintaing the gradient of Ca2+?

Answer 2

Relative impermability of the plasma membrane, expulsion of calicium across the plasma membrane and calcium buffers

Question 3

What are the two channels used to expel calcium over the membrane/

Answer 3

The ca2+ATPase and the Na+/ca2+ exchanger

Question 4

How does the Ca2+ATPase channel work?

Answer 4

It is a high affinity, low capcity channel, whihc works well at lower calcium ion concentrations, it operates via a feedback mechanism where ca2+ increases, binds to calmoduiln, this complex binds to Ca2+ATPase and then this is expelled across the membrane.

Question 5

What are some of the features of the NCX channel?

Answer 5

It is a low affinity, higher capcity channel, it is an antiporter, using the Na+ gradient to drive the expulsion of Ca2+ from the cell, and is electrogenic and therefore works best at the resting membrane potential

Question 6

What are the two types of calcium stores that are found in the cell?

Answer 6

Rapidly reasable and non-rapidly realeasable

Question 7

What are trigger proteins?

Answer 7

A protein that binds to ca2+ and alters its function

Question 8

What are some examples of trigger proteins?

Answer 8

Synaptomogmin, calmodulin, troponin

Question 9

What are Ca2+ buffers/

Answer 9

They limit the diffusion of atp and Ca2+ by binding to them does not cause changes in calcium just regulates the activity of the calcium

Question 10

What are the two receptor types involved with calcium influx across a receptor membrane?

Answer 10

Voltage operated calcium channels and iontropic receptors

Question 11

What sort of membrane receptors are iontropic receptors?

Answer 11

Ligand gated

Question 12

What mechanism increases calcium in the endoplasmic reticulum?

Answer 12

The SERCA pump

Question 13

How are the IP3 calcium channels on the endoplasmic reticlum opened?

Answer 13

A ligand attaches to a g protein coupled receptor on the cell surface membrane, this goes on to active PIP2 which goes on to create IP3 through a chain of reactions, and therefore causes the release of calcium from the intracellular receptors

Question 14

What receptors are involved in calcium induced calcium realease?

Answer 14

Ryanodine

Question 15

How is calcium induced calcium release used in the cardiac myocytes?

Answer 15

Ca2+ entry through the VOCCs after depolarisation,, Ca2+ acts on ryandoine receptors that are on the endoplasmic reticulum close to the plasma membrane of the cell and cause the release of calicum

Question 16

How is Ca2+ regulated by the caridac myocyte?

Answer 16

During the early part of the action potential, the NCX pump reverses but as the cocentration of calcium rises, extrusionn in the NCx pump is favoured to remove Ca2+. Ca2+ is also returned to the endoplamsic retlicum by SERCA to prepare for another event

Question 17

What is the main non rapidly reverisble store of calcium?

Answer 17

Mitochondria

Question 18

How does the mitochondria uptake calcium?

Answer 18

It is via a uniporter, which is driven by the repiration proton production chain, which is a low affinity high capcitiy pump.

Question 19

What conidtions is mitochondrial calcium overload key in?

Answer 19

Triggering cell death, such as in Ischaemic and traumatic brain injury, alhzmiers, Parkinson’s.

Question 20

What is the role of calcium in muscle contraction?

Answer 20

it binds to topoinin which undergoes a conformational change that causes tropomusin to move, and reveal the binding sites for myosin head groups that go on to cause muscle contraction

Question 21

How does a capative and store operated chain?

Answer 21

Proteins in the ER membrane such as STIM (which is an ER membrane located Ca2+ sensor) and ORA1 which is a plasma membrium sensor, whihc ends depletion signals to activate channels to increase calcium concentration in the ER

Question 22

What do you require for to return calcium into the cell into the basal layer?

Answer 22

Termiantion of signal, Ca2+ store refilling and Ca2+ removal

Question 23

What are the advantages of a large inward gradient of calcium?

Answer 23

changes in the concentration of calcium can occur rapidly with little change in the concentration of calcium, and little has to be done to restore the resting condition