The aquaporins (AQP), also known as the major intrinsic protein superfamily (MIP), are a family of integral membrane proteins. In mammals, 13 aquaporins were described (AQP0–AQP12). Aquaporin 11 (AQP11) is a newly described member of the aquaporins family. Aquaporin 11 (AQP11) has been identified with unusual pore-forming NPA (asparagine-proline-alanine) boxes. AQP11 presents a conserved structure of six transmembrane domains with intracellular N- and C-termini. The functional channel is a tetramer but each subunit has a separate pore and therefore the functional channel unit, contains four pores¹. There are two subfamilies: the aquaporins, which transport only water and the aquaglyceroporins, which transport glycerol, urea, and other small solutes in addition to water².

Aquaporins and aquaglyceroporins are ubiquitously expressed, including in the plasma membrane of renal epithelia, brain astrocytes, and red blood cells³.  AQP11 is expressed in several tissues including testis, kidney, liver, and brain. In the brain, AQP11 is found in Purkinje cells, hippocampal neurons of CA1 and CA2, and cerebral cortical neurons⁴. In the kidney AQP11 has a central role in vesicular homeostasis as demonstrated in experiments using AQP11 knockout mice which display growth retardation and progressively die before weaning. The cause of death seems to be advanced renal failure⁵.