The aquaporins (AQPs) are a family of integral membrane proteins composed of two subfamilies: the orthodox aquaporins, which transport only water, and the aquaglyceroporins, which transport glycerol, urea, or other small solutes []. AQP1 in pleural mesothelial cells participate in the formation of pleural fluid [], renal AQP2 is involved in levels of solutes []and changes in AQP9 in the hippocampus are related to delayed neuronal death []. Aquaporins contain two tandem repeats, each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA).Aquaporin-11 and aquaporin-12 (AQP12) belong to a new aquaporin subfamily termed superaquaporins []. AQP12 is exclusively found in pancreatic acinar cells [], and is not localised in the plasma membrane. No specific localisation has yet been established for this subfamily, but its presence in the pancreas implies some role in the secretion of digestive enzymes []and fluids in the pancreatic cells []. A structural characteristic of AQP12 is the lack of a cytoplasmic N-terminal region, by contrast with all other known aquaporins.
