Chloride
At least eight families of chloride channels have been identified as membrane or intracellular chloride channels/binding proteins; they include the ligand-gated chloride channels (e.g., GABAA and glycine), cystic fibrosis transmembrane conductance regulator (CFTR), CLC, bestrophins, calcium-activated chloride channel regulator (CLCA), chloride intracellular channel (CLIC), Tweety, and the most recently characterized TMEM16/anoctamin family. Only the latter four of these chloride channel families contain members regulated by calcium[1]. Calcium activated Chloride Channels (CaCCs) are anion-selective channels that are activated by increases in cytosolic Ca2+. They have been implicated in a variety of cellular functions such as fertilization of the oocyte, transepithelial fluid transport, repolarization and action potential duration in cardiac myocytes, olfactory transduction, and regulation of smooth muscle tone. Within the airways, they contribute to epithelial fluid secretion.[2]
[1] G Gallos et al. Calcium-Activated Chloride Channels. Chapter in “Calcium Signaling In Airway Smooth Muscle Cells”. Y.-X. Wang (ed.), Springer International Publishing Switzerland 2014.
[2] J Eggermont et al. Calcium-activated chloride channels: (un)known, (un)loved? Proc Am Thorac Soc. 2004;1(1):22-7.