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calcium ions

• ca2+ binding can alter the local electrostatics within a protein bacause of its shape and charge
• this can cause a conformational change in protein which can alter the surface/structure of the protein
• therefore, ca2+ can mediate signaltransduction within a cell

calcium homeostasis

• the concentration of free Ca2+ within the cytosol of the cell is tightly regulated

1. extremely high levels are toxic and lead to cell death
2. reduce background noise - so Ca2+ can act as a second messenger

a resting cell

• the Ca2+ concentration is low in the cytosol
• ca2+ pumps and Ca2+ exchangers
• ca2+ pumps incude:

1. plasma membrane Ca2+ATPase (PMCA)
2. smooth endoplasmic Ca2+ATPase (SERCA)

• Ca2+ exchangers include:

1. Na+/Ca2+ exchanger (NCX)
2. Na+/Ca2+/K+ (NCKX)

calcium entry

1. volatge gated Ca2+ selective channels (CaV)

a change in voltage can cause each channel to conduct roughly a million Ca2+ ions per second down the 20,000-fold gradient

2.transient receptor potential (TRP) ion channels

• located in the plasma membrane
• permeable to cations
• sensory tranduction

3. Ca2+ release activated calcium (CRAC) channels

• located in the plasma membrane
• a component of this channel - ORAII
• ORAII is able to interact with a second protein - STIMI
• STIM I is able to detect when ER Ca2+ is low
• STIMs can also activate some TRPs

-so this pathway is used to replenish ER Ca2+…