Final answer:
Store-operated calcium channels open in response to changes in cytoplasmic Ca²+ concentration. They are activated when the endoplasmic reticulum becomes depleted and allow the influx of calcium from outside the cell. This process triggers various cellular responses depending on the cell type.
Step-by-step explanation:
Store-operated calcium channels open in response to changes in cytoplasmic Ca²+ concentration. These channels are activated when the endoplasmic reticulum, which stores calcium ions, becomes depleted and triggers the influx of calcium from outside the cell. Ligand-gated calcium channels allow the higher levels of Ca²+ outside the cell to flow into the cytoplasm, leading to various cellular responses depending on the cell type. For example, in ß-cells of the pancreas, Ca²+ signaling leads to the release of insulin, while in muscle cells, an increase in Ca²+ leads to muscle contractions.