What is the role of inositol 1,4,5-triphosphate (IP3) in the Phosphoinositide Signaling Pathway?

• A. It directly activates phospholipase C.
• B. It activates protein kinase A.
• C. It phosphorylates target proteins in the cytoplasm.
• D. It binds to calcium channels in the endoplasmic reticulum, releasing Ca2+ into the cytoplasm.

Answer: (D)