Final answer:
True, Ca2+ ions act as second messengers in cell signaling, being released into the cytoplasm upon signaling to trigger various cell-specific responses.
Step-by-step explanation:
True, ions like Ca2+ can indeed serve as second messengers in cell signaling. The concentration of calcium ions within a cell is usually kept low through the action of ion pumps in the plasma membrane that use ATP to remove Ca2+. However, when signaling occurs, such as in response to a ligand binding to a receptor, Ca2+ stored in vesicles like the endoplasmic reticulum or from the extracellular space can be released into the cytoplasm.
Increased cytoplasmic calcium levels trigger a variety of responses, depending upon the cell type. For instance, in the ß-cells of the pancreas, this can lead to the release of insulin, whereas in muscle cells it can result in muscle contractions. Furthermore, Ca2+ can activate various enzymes or bind to proteins like calmodulin to further propagate the signaling cascade.