Calcium ion channel
Calcium ion (Ca2+) channels are protein channels are only permeable to Ca2+.Calciuim ion channels are mainly found in the membrane of cells and organelles such as the sarcoplasmic reticulum, phospholipid bilayer of the cell surface membrane and many more. There are many types of calcium ion channels that exist in eukaryotic and prokaryotic cells. There are the voltage-gated ion channels and ligand-gated ion channels.
References: Alberts, B., Johnson, K., Lewis, J, Raff, M., Roberts, K.. Walter, P (2008). Molecular Biology of the Cell, Fifth Edition, New York: Garland Science. 912-913