Description
Aquaporin 3 is the third member of the major intrinsic protein family. The protein is localized at the basal lateral membranes of collecting duct cells in the kidney. AQP3 appears to exist as a single copy and to comprise 6 exons distributed over 7 kb. The gene is mapped to 9p21-p12 by fluorescence in situ hybridization. The protein works as water-channel and facilitates the transport of nonionic small solutes such as urea and glycerol, albeit to a smaller degree. The results suggested that water channels can be functionally heterogeneous and possess water and solute permeation mechanisms. By Western blot analysis and immunofluorescence microscopy of epidermis, Sougrat et al.(2002) showed strong expression of an approximately 33-kD glycosylated AQP3 protein in keratinocyte plasma membranes, one layer below the unstained stratum corneum(SC). It provides a short circuit for water, or water-clamp, between the base of the epidermis and the SC in order to maintain a constant H2O content and to prevent the formation of a continuous water gradient across the epidermis below the SC