Forms a water-specific channel; mercury-sensitive. It may have an important role in spermatogenesis, in fertilization, and in the secretion of pancreatic juice and saliva. Highly expressed in sperm, pancreas and liver. Some expression has been found in salivary gland and absorptive colonic epithelial cells. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family.