Final answer:
Calcium's role as a second messenger leads to an increase in cytoplasmic Ca²+ concentration, affecting various cellular processes, including hormone secretion and muscle contraction.
Step-by-step explanation:
When calcium is utilized as a second messenger in cellular signaling, the concentration of calcium (Ca²+) in the cytoplasm increases. This mainly occurs through the opening of ligand-gated Ca²+ channels that allow Ca²+ to flow from areas of higher concentration outside the cell or from storage within the cell into the cytoplasm. Cellular responses to the increased Ca²+ levels can vary, such as stimulating insulin release in pancreas ß-cells or triggering muscle contractions.
Calcium ions are kept at low levels in the cytoplasm due to the activity of ion pumps in the plasma membrane that continuously remove Ca²+ using ATP. For signaling, Ca²+ is stored in vesicles like the endoplasmic reticulum. Activation of phospholipase C (PLC) in response to G protein-coupled receptor signaling leads to production of inositol triphosphate (IP3), which causes the release of Ca²+ from the endoplasmic reticulum into the cytoplasm, further elevating Ca²+ levels and activating various cellular processes either directly or via calcium-binding proteins like calmodulin.