Cytosolic calcium normally is kept extremely low (~100 nM); the ER and extracellular fluid hold large stores.
Phospholipase C cleaves PIP₂ into DAG and IP₃. The role of IP₃ is to:
- A
Inhibit adenylyl cyclase
- B
Phosphorylate the receptor
- C
Activate PKA
- Dcheck_circle
Open Ca²⁺ channels in the ER, releasing Ca²⁺ into the cytosol
Explanation
IP₃ diffuses to the ER and binds IP₃ receptors (Ca²⁺ channels), allowing Ca²⁺ to flood the cytosol—where it acts as a second messenger.