Small intracellular mediators relay signals from cell surface receptors to various intracellular targets, amplifying the cellular responses to extracellular signals. They do this by binding to and influencing the behavior of target proteins. Examples of small intracellular mediators include: Ca2+, cyclic AMP, and diacylglycerol. Cyclic AMP and Ca2+ are water-soluble and diffuse within the cytosol, while diacylglycerol is lipid-soluble and diffuses along the plasma membrane.