Polycystin 2 (PKD2), the product of the gene mutated in type 2 autosomal dominant polycystic kidney disease, belongs to the polycystin family. PKD2 is a ~110-kDa six-transmembrane channel protein with cytoplasmic N- and C-termini. This protein functions as a Ca2+-activated intracellular Ca2+ release channel in the endoplasmic reticulum. It is also present in the plasma membrane, where it functions as a nonselective cation channel. In addition, PKD2 expression has been documented in the primary cilium of kidney epithelial cells, where it is believed to have an essential role in mediating Ca2+ entry in response to flow rate changes, suggesting that it may be part of a mechanosensing machinery residing in the primary cilium. (PMID: 16135816; 10497221)