In a cell signaling pathway, IP3 is produced and diffuses into the cytoplasm. What is the next step in this pathway?

• A. IP3 is converted back into PIP2 in the cytoplasm.
• B. IP3 binds to the cell membrane to initiate endocytosis.
• C. IP3 binds to calcium channels on the endoplasmic reticulum, causing them to open and release calcium ions into the cytoplasm.
• D. IP3 directly activates protein kinase C in the cytoplasm.

Answer: (C)