Answer:
4. calcium ion and cAMP
Explanation:
Second messengers are the intracellular chemicals that are produced for signal transduction and generation of cellular response when a water-soluble hormone binds to its cell surface receptors. Since water-soluble signaling molecules such as protein hormones cannot cross the cell membranes of their target cells, their binding to the respective receptors triggers the production of an intracellular second messenger. The most common second messenger molecules are cAMP and calcium ions. For example, protein hormones bind to their G-protein linked membrane receptors and trigger the synthesis of cAMP in their target cells.
