IPC Time Course Flashcards
Ca2+ concentration in ER lumen vs cytosol
At rest, the concentration of free Ca2+ in the ER lumen is thought to be several hundred µM (~250 µM; Meldolesi and Pozzan 1998; Corbett and Michalak 2000), a thousand times or more greater than the resting cytosolic level.
What maintains Ca2+ concentration gradient?
SERCA pumps that actively transport Ca2+ into the ER from the cytoplasm, thereby recycling previously liberated Ca2+ and assisting in the clearance of excess Ca2+ entering across the plasma membrane
In what way is SERCA Ca2+ sensitive?
SERCA pumps are sensitive to cytosolic and ER Ca2+ levels and “turn on” in the excess of the former or insufficiency in the latter
What proteins in the ER regulate Ca2+ concentration?
A special set of Ca2+ buffers, such as calreticulin, calsequestrin, and calnexin, that help determine and stabilize the free Ca2+ level in the ER and determine the total amount of releasable Ca2+ (Corbett and Michalak 2000)
In what way do M1R’s and B2R’s respond in non-excitable cells? (and who?)
Stimulation of either of these two receptors leads to PLC-mediated production of IP3, which triggers release of Ca2+through ER-associated IP3R’s (Felder, 1995)
In what way do M1R’s and B2R’s respond in neurons and what are the implications of this?
Only B2Rs produce a significant rise in intracellular Ca2+
only the B2R efficiently couples to the endoplasmic IP3R
How was the differential response between M1R’s and B2R’s investigated and by who?
Through dynamic tracing of receptor-mediated PLC signals in individual neurons in combination with patch-clamp recording of macroscopic and microscopic membrane domains
Delmas et al., 2003
What causes the differential response between M1R’s and B2R’s?
A membrane arrangement that links IP3Rs to B2Rs, but not M1Rs, allowing IP3 to be produced at the required concentration and the precise location inside the cell
How might PIP2 be involved in mediated differential responses of GqPCR’s?
Differential Ca2+i signals underlying receptor-specific stimulation of PIP2 synthesis by stimulation of PI 4-kinases by Ca2+
What binding protein inhibits IP3 signalling?
IP3-binding protein released with IP3 (IRBIT) acts as a competitive antagonist
What happens when we reduce levels of IRBIT and who showed this?
Allow Ca2+ release at lower concentrations of IP3 (Ando et al. 2014)
What does expressing dominant negative IRBIT do to M1R’s and who showed this?
Zaika et al.,2011 found that expressing dominant negative IRBIT allowed M1Rs to evoke Ca2+ release through IP3Rs.
What types of post-translational modifications can occur to IP3R’s?
Post-translational modification of IP3Rs by associated proteins may be reversible (e.g. phosphorylation) or irreversible (e.g. proteolysis and some covalent modifications).
What covalent modification inhibits IP3R’s?
Ca2+-dependent enzyme transglutaminase type 2 covalently modifying a glutamine residue within the C-terminal tail of IP3R1
How does TGM2 covalent modification prevent IP3R activation and who showed this?
causes irreversible cross-linking of adjacent IP3R subunits via a lysine residue and the modified glutamine. This prevents the conformational changes required for activation of IP3Rs, and so inhibits IP3-evoked Ca2+ release (Hamada et al. 2014)
