title: Immunohistochemical Localization of the Water Channels AQP4 and AQP5 in the Rat Pituitary Gland.
abstract: The pituitary gland is composed of the adenohypophysis and neurohypophysis. The adenohypophysis contains endocrine cells, folliculo-stellate (FS) cells, and marginal layer cells, whereas the neurohypophysis mainly comprises axons and pituicytes. To understand the molecular nature of water transfer in the pituitary gland, we examined the immunohistochemical localization of the membrane water channels aquaporin-4 (AQP4) and AQP5 in rat tissue. Double immunofluorescence analysis of AQP4 and S100 protein, a known marker for FS cells, marginal layer cells, and pituicytes, clearly revealed that FS cells and marginal layer cells in the adenohypophysis and the pituicytes in pars nervosa are positive for AQP4. AQP5 was found to be localized at the apical membrane in some marginal layer cells surrounding the Rathke's residual pouch, in which AQP4 was observed to be localized on the basolateral membranes. These results suggest the following possibilities: 1) FS cells especially require water for their functions and 2) transepithelial water transfer could occur between the lumen of Rathke's residual pouch and the interstitial fluid in the adenohypophysis through the AQP4 and AQP5 channels in the marginal layer cells.
authors.affiliation: Department of Anatomy and Neurobiology, Graduate School of Medicine, Nippon Medical School, Bunkyo-ku, Tokyo 113-8602, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsuzaki
authors.forename: Yuki
authors.initials: Y
authors.lastname: Inahata
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sawai
authors.forename: Chun-Ying
authors.initials: CY
authors.lastname: Yang
authors.forename: Makito
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Takata
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ozawa