Intercellular ion homeostasis 1 Flashcards
How can we find calcium ions in cytosol?
free, bounded to proteins and bounded to surfaces of membranes
By what is calcium conc. regulated?
by transporters located in plasma memb, memb of ER/SR and inner mitochondrical memb.
What creates great electrochem. driving force for Ca to eneter cytosol in plasma memb?
difference in extracellular (2mM) and intracellular (100nM) calcium conc. Ca is carried by passive Ca transporters (ion channel).
What kind of transporter is used to move ions from intra- to extracellular space in plasma memb?
active transporters
What transporters are getting back Ca back to ER/SR ?
SERCA - primary active, ATP driven pump
How many trenaporters are in inner mitochonrial memb?
2 secondary activet transporters (Na+/Ca2+ and H+/Ca2+ (antiports)) and 1 Ca2+ channel (MCU)
At how much nM is cytosolic free Ca maintained at?
100-200nM
Main Ca2+ entry mechanisms? Explain!
- plasma membrane (powered by electrical and chemical gradient, gated by voltage, ligand and stretch ion channels in plasma memb. conc of Ca2+ is 2mM)
- intracellular membrane (Ryanodine receptor and IP3 receptor, powered by chemical gradient and its gated by intracellular ligands.) Mechanism: Ca2+ ions are coming from the store into the cytosol. Ic ligand gating binds in order to open ion channel and entry of ions carried w chem. gradient
When do we have positive feedbackof intracellular Ca2+ release channels?
Whenever ion channels open and Ca2+ is going to be released and Ca2+ conc. is less than 300nM -positive feedback, it will get many more Ca2+ out of the store.
When do we have negative feedback of intracellular Ca2+ release channels?
Whenever we pass 300nM Ca2+ will inhibit
What is Ryanodine receptor?
Intracellular ligand gated Ca2+ channel located in the memb of SR/ER. Its activating channel in skeletal muscle cells in part of DHP receptor.
Diff bt/w SR and ER?
ER synthesizes molecules
SR stores calcium ions and pumps them out into the sarcoplasm when the muscle fiber is stimulated.
Signals in skeletal muscle, explain!
By depolarization, Ca2 conc. increases. Coupling is done by 2 proteins (by protein - protein interaction): DHP and Ryanodin receptor.
Depolarization - DHP receptor changes its conformation - Its hooked to RYR -pulls on receptor - open.
Signals in neurons/cardiac muscle, explain!
RYR not attached to the memb. communication btw RYR and depolaziration on Ca2+ signal is mediated by voltage-gated Ca2+ channels. - Ca2+ binds RYR and trigger its release.
NOTE: IN THIS CASE LIGAND IS Ca2+ ITSELF!!!
Signals in all cells, explain!
Interaction bt/w extracellular ligand and receptor in order to increase Ca2+ conc. Mediated by RECEPTOR LIGAND INTERACTION in plasma memb. - starts enzymatic activity (will result in small lipid derivative signaling molecule = IP3 receptor), - it will reach IP3 and start release of Ca2+.
