Which second messenger causes the release of calcium ions (\(\mathrm{Ca^{2+}}\)) from the endoplasmic reticulum?

• A. Cyclic adenosine monophosphate (cAMP)
• B. Diacylglycerol (DAG)
• C. Inositol 1,4,5-trisphosphate (IP\(_3\))
• D. Guanosine triphosphate (GTP)

Answer: (C)

Verified step by step guidance

1. Understand the role of second messengers: Second messengers are molecules that relay signals received by receptors on the cell surface to target molecules inside the cell. They play a critical role in signal transduction pathways.
2. Identify the second messenger responsible for calcium ion (\(\mathrm{Ca^{2+}}\)) release: Among the options provided, the second messenger that directly triggers the release of calcium ions from the endoplasmic reticulum is Inositol 1,4,5-trisphosphate (IP\(_3\)).
3. Explain how IP\(_3\) works: IP\(_3\) is produced when a signaling molecule activates a receptor, which in turn activates phospholipase C. Phospholipase C cleaves a membrane phospholipid (PIP\(_2\)) into two products: diacylglycerol (DAG) and IP\(_3\).
4. Describe the action of IP\(_3\): IP\(_3\) binds to IP\(_3\) receptors on the membrane of the endoplasmic reticulum. This binding opens calcium channels, allowing \(\mathrm{Ca^{2+}}\) ions to flow from the endoplasmic reticulum into the cytoplasm.
5. Summarize the importance of \(\mathrm{Ca^{2+}}\) release: The increase in cytoplasmic \(\mathrm{Ca^{2+}}\) concentration acts as a signal for various cellular processes, such as muscle contraction, secretion, and cell signaling pathways.