Control Of Cytosolic Calcium Flashcards
Name some functions of calcium
Apoptosis Muscle contraction Neurotransmission Gene regulation Memory (LTP)
Equilibrium potential of calcium?
+123mv
What are the intracellular and extracellular conc of calcium?
Intra = 10^-7M Extra = 1-2mM
What are the advantages of a large calcium gradient?
Small influx = large conc difference
Little has to be removed to re establish resting calcium
Disadvantages of large calcium gradient?
maintaining gradient is energy expensive
Easy to overload and lead to cell death
How is the calcium gradient set up and maintained?
Plasma membrane Ca2+ ATPase
NCX
Calcium buffers
What are come characteristic of the PMCA?
High affinity, low capacitance
Therefore works when levels of calcium are low and does not shift large amounts
Uses ATP
Also regulated by calcium calmodulin complex. Increase in calcium increase complex binding to PMCA which stimulates it to remove calcium
What direction does the PMCA move calcium?
Extracellularly
What direction does the NCX move ions?
RMP = 3Na+ in 1Ca2+ out
Depolarisation reverses this
Where are some characteristics of NCX channels?
Powered by secondary activity transport by sodium gradient set up by Na+K+ATPase
High capacity low affinity
Channel is electrogenic (net + influx) means sodium harder to move in at more positive mV
Name some calcium buffers?
Calsequestrin
Parvalbumin
Calbindin
What do calcium buffers do?
Bind to calcium with no intrinsic function to slow down rise in intracellular calcium and prevent global cellular rise by maintaining calcium rise in micro-domain (within 0.1-05(micro)m)
What are calcium trigger proteins?
Bind calcium which causes an altered effect on protein
E.g. Synaptotagmin in neurotransmission
Explain synaptotagmins (ST) role in neurotransmission
ST is a V-SNARE which has a C2A and C2B domain on the cytosolic side
These bind calcium (C2a = 3 calcium, C2B = 2 calcium)
Calcium bind here follows VGCC opening which causes conformational change which allows it to interact with syntaxin (t-SNARE)
Allows for fusion
How is elevation of intracellular calcium achieved?
VOCC
Ionotropic glutamate receptors
GPCRs coupled to Gq
Calcium induced calcium release
What are some characteristics of VGCC?
Many types (N,L,P/Q,R)
Modulated by PKC
Alpha 1 subunit = 6TMDs made of 4 connected domains
May have accessory subunits
What ionotropic glutamate receptors allows calcium influx?
NMAR
AMPAR (those without GluA2 subunit)
How does Gq couples GPCRs increase calcium?
Formation of ip3 which acts on IP3R on SER
Note SERCA uses ATP to restore calcium stores in SER
Where can calcium come from to cause CICR?
VGCC
Ionotropic receptors
Intracellular stores
What receptors does calcium act on on the SER?
Ryanodine
Where does CICR occurs?
Skeletal muscle Cardiac myocytes (approx 80% comes from intracellular stores)
What is another ligand for ryanodine receptors?
Cyclic adp ribose
What is the role of the mitochondria in calcium levels?
Can uptake via a calcium uniporter deals with high concentrations within a microdomain (act as a buffer) Low sensitivity (low affinity , high capacity)
How is the mitochondria important in calcium modulation?
Calcium amplification
Spaciotemporal signalling
What is calcium moved to after taken up by mitochondria?
The ER
What is the role of calcium in the mitochondria?
Stimulates mitochondrial metabolism (rise in Ca2+ signals more ATP needed to pump out) Cell death (PD) BCL-2 important of calcium handling
How is basal calcium returned to normal?
Termination of calcium signal
Calcium removal
Calcium store refill
How is the SER refilled with calcium after depletion?
Ca2+ not bound to EF hand motif on internal surface of STIM1 in ER
This allows STIM1 aggregation (normally inhibited by Ca2+)
STIM1 interact with eachoether via coiled coil domain
Cytosolic STIM1 then interacts with Oria 1 channel (Store operated calcium channel) which allows ca2+ entry
SERCA then pumps calcium into SER
Calcium binds to STIM1 EF hand motif and causes uncoupling of oria1 and STIM1
It what cell types do storage operated calcium channel sfunction in?
Non excitable cells and excitable cells
What 3 techniques can be used to measure intracellaul Ca2+?
Radioisotope
Electrophysiology
Fluorescent calcium indicator
What fluorescent indicator can be used to measure calcium?
Fluo-4
Since fluo-4 cannot pass through the cell memebrane how must it be administered?
Microinjection directly into cell
Given as fluo-4 acetoxymethyl ester which is degraded by intracellular esterases into Fluo-4
What happens when calcoum binds to fluo-4
It fluoresces which allows visualisation of calcium levels in real time
What are the different types of calcium signals?
Wave
Blip
Puff
How can calcoum regulate so many processes?
Differences in space, time and amplitude
How does space dictate the processes calcium regulates?
Space is dependant on calcium influx which can be different places in the cell e.g. Localised to intracellular store or plasma membrane
Five an example of global and elementary increases in calcium
Global - gene transcription and muscle contraction
Elementary - microdomains, neurotrasmission
How can time regulate calcium signalling?
Can be a transient or prolonged increases which have different effect.
Transients avoid cell death
Prolonged calcium signalling may be inflated in cell death, cell proliferation and inflammatory response
What can influence calcium pattern over time?
Different receptors show different calcium concentration patterns over time upon activation
This may produced different effects and modulate what a cell does in responce to receptor activation
How does amplitude regulate how calcium modulates many cellular responses?
Strength of signal related to site of transient
