5.2 Control of Cytosolic Calcium Flashcards
List 4 ways the cell controls and maintains the [Ca2+]i
The membrane is relatively impermeable to Ca2+ ions
Cells can expel Ca2+ across the plasma membrane
Ca2+ buffers
Intracellular Ca2+ stores
Give an advantage and a disadvantage of signalling using Ca2+
Advantage: changes in intracellular Ca2+ occur quickly with little movement of Ca2+
Disadvantage: Ca2+ overload leads to loss of regulation and cell death
Describe the action of Ca-ATPase
If [Ca2+]i increases, the Ca2+ will bind to calmodulin. The complex then binds to Ca2+ - ATPase. ATP is required to transport 1 Ca2+ ion OUT of the cell. It has a high affinity and a low capacity.
Describe how the Na-Ca-exchanger works
The NCE works on the Na+ gradient and is electrogenic. It works most efficiently at resting potential. 1 Ca2+ is moved OUT and 3 Na+are moved IN. It has a low affinity but a high capacity.
Describe the actions of a VOCC
VOCC: voltage-operated calcium channel
When the membrane depolarises, the VOCC open and Ca2+ moves IN to the cell.
Describe the actions of a receptor-operated Ca2+ channel
A ligand binds to the Ca2+ channel and opens the pore.
Describe the actions of a SERCA pump
A Ca2+ - ATPase pump on the ER membrane. Ca2+ is driven against its concentration gradient. Calmodulin is not used.
Describe the process of G-protein coupled receptor Ca2+ release
The stimulated G-protein causes an intracellular cascade.
aq => phospholipase C => IP3 => increased [Ca2+]i via S/ER stores
as/ai => adenyl cyclase => cAMP => protein kinase A
Describe the action of CICR proteins
CICR: Ca2+ induced Ca2+ release
Ryanodine receptors on the ER open to Ca2+ when Ca2+ binds to them. The Ca2+ is from the depolarisation of the cell.
What is the role of mitochondria in Ca2+ release?
Mitochondria can take up excess Ca2+ when Ca2+ is very high. They act as Ca2+ buffers.
How are the intracellular Ca2+ stores refilled?
The stores are refilled by:
Recycling of released Ca2+
VOCC
