Intracellular Calcium Homeostasis Flashcards
What is the typical resting Ca concentration in the cytosol?
50-100nM
How do cells keep IC calcium low?
PM Ca-ATPase, ER-Ca-ATPase, mitochondrial high capacity(low affinity) pump - when IC is very high, existence of Ca binding molecules in cytoplasm reducing free Ca
What are the pumps that exist on the ER and mitochondrial membrane for keeping Ca low?
Ca-ATPase, NCX, Ca-binding molecules
What are the pathways for IC calcium increase?
VGCC, ROCC, NCX, Ca-ATPawe of SER and PM, Ca release channels on SR and ER
What does the removal of K via of BK channels do to IC Ca?
causes VGCC and ROCC to close
How can calcium be released from Internal stores?
ligand binding to GPCR - Gq - PLCB1 catalysis hydrolysis of PIP2 which produces IP3 and DAG - IP3 release Ca from ER
What is the effect of lithium on PIP2 metabolism?
inhibits enzymes involved in the recycling of phosphoinositols which blocks the regeneration of PIP2 and therefore depletes PIP2
overactivity of PIP2 can result in mania so lithium can treat this but may affect other organ functions
What is the main subtype of IP3R in the brain?
IP3R1
How is the depletion of IC calcium stores sensed?
STIM proteins
What channels are activated by STIM proteins to stimulate store refilling?
ORAI proteins
Which drugs can be used to prevent Ca requestration into stores?
thapsigarin or CPA
What is the difference between STIM 1 and STIM 2?
STIM1 is a sensor of store depletion where STIM2 senses basal ER levels
How are ORAI proteins stimulated?
the C domain of the ORAI is stimulated by STIM. EF hand senses the availability of Ca, low affinity so high Ca will bind when store full and releases when depleted
STIM releases Ca when depleted and initiates a process leading to CRAC channel activation
mutants of EF hand show this is its function
Where does STIM1 bind?
the microtubule of the end binding protein 1
How does the cell respond to sudden changes in energy demand?
by sensing an increase in mitochondrial Ca
What happens when the mitochondria is overloaded with Ca?
causes the opening of a high conductance channel, the mitochondrial permeability transition pore (PTP) leading to collapse of proton gradient and ATP production, loss of mitochondrial membrane integrity and some forms of cell death
What are the main pathways for Ca entry and exit form the mitochondria?
Mitochondrial calcium uniporter - low conductance, low affinity
mitochondrial NCX
mHCX
mPTP - may activate Ca dependent proteases wsuch as calpaan to initiate cell death
Why are mitochondria placed close to ER/SR?
can sense local intracellular Ca conc. and serve as sensors of cellular Ca signals MFN2 helps form mitochondria ER contacts
MAMs are where the ER and mitochondrial Ca channels interact
how might mitochondria be positioned in a neuron?
they may be positioned near Ca conduction channels to ensure that the accumulation of Ca does not cause a cytosolic Ca wave
What are some of the spatial and temporal aspects of Ca signalling?
transient Ca may be localised and specifically regulate only nearby target e.g. NT release
Ca ions ca propagate as a wave throughout a cell e.g. to communicate signals to the nucleus i.e. at fertilisation
(if sustained this can cause neurotoxicity so waves are infrequent)
What are the two binding sites on the IP3R?
one high affinity binding site for Ca to stimulate further release and one low affinity binding site to reduce Ca release in high concentrations
How does Ca affect CaM?
has 4 Ca binding sites and the binding of Ca increases its affinity for other target enzymes
How does Ca-CaM modulate Ca-CaM dependent Kinase II?
Ca-CaM removes the auto inhibitory domain for the catalytic site resulting in autophosphorylation and activation of the AMPAR increasing its current and adding new AMPAR to the synapse
Constituitively active before but Ca-CaM increases activation
important in LTP and concentrated in post-synaptic density
in low calcium conditions calmodulin dissociates after 10s
What is the role of Calcinuerin in LTD?
Ca-CaM activates Calciuneurin which is a dependent phosphatase and regulates a phosphatase, phosphatase 1.
inhibition of Calcineurin blocks induction of LTD
LTD results from removal of AMPAR by endocytosises
What are some methods of measuring CA?
radioactive labels - not great as no spatial/temporal info
ion-sensitive micro electrodes - no spatial info
indirect electrophysiology - Ca dependent currents
NMR spectroscopy
Ion-sensitive dyes
