Aquaporin 8 (AQP8) belongs to the family of aquaporins, which are small membrane-bound integrated proteins associated with major intrinsic proteins (MIPs, i.e. AQP0). In the plasma membrane of renal tubules, AQP8 mediates the permeation and transport of water to the bile duct, promoting cAMP induced bile duct water secretion and playing a key role in bile formation. In addition, AQP8 also mediates the release of hydrogen peroxide from liver cell mitochondria, regulates cholesterol synthesis mediated by sterol regulatory element binding protein 2 (SREBF2), and promotes mitochondrial uptake of ammonia (mainly metabolized into urea under glucagon stimulation). AQP8 may play an important role in the adaptive response to acidosis in proximal renal tubular cells, possibly by promoting mitochondrial ammonia transport.
