Immunolocalization of Aquaporin-8 in Rat Digestive Organs and Testis.

Abstract

Expression of aquaporin-8 mRNA has previously been shown in hepatocytes, pancreatic acinar cells, colon epithelial cells and seminiferous tubules of the testis in the rat by in situ hybridization technique. However, immunolocalization of this water channel has not yet been demonstrated. In the present study, the localization of immunoreactive aquaporin-8 and expression of the mRNA were examined in rat organs (cerebrum, cerebellum, eye, salivary gland, heart, lung, liver, pancreas, esophagus, stomach, jejunum, ileum, colon, testis, ovary, kidney, spleen and lymphnode) by immunohistochemistry using an antibody against aquaporin-8 and ribonuclease protection assay. Aquaporin-8 was distinctly immunolocalized on the apical membranes of pancreatic acinar cells and mucosal epithelium of the colon and jejunum. In the liver, the bile canalicular membrane of hepatocytes was immunostained. In the testis, immunoreactive aquaporin-8 was demonstrated on the luminal side of the seminiferous tubules. At high magnification, the peroxidase reaction products appeared on the ramified cytoplasmic membrane of Sertoli cells surrounding the residual bodies or spermatogenic cells. Specificity of the antibody was verified by Western blot analysis showing a minor approximately 28 kDa band (deduced deglycosylated form of aquaporin-8) and a major approximately 30 kDa band (glycosylated form) in these organs. The intensity of aquaporin-8 immunoreactivity was approximately comparable to that of aquaporin-8 mRNA expression in the liver, pancreas, colon, jejunum and testis. The aquaporin-8 mRNA expression in the hepatocytes was presumed to be closely associated with the structure of bile canaliculi since the message was detected in hepatocytes immediately after isolation from the liver but not in cells following cultivation for three days. The localization of immunoreactive aquaporin-8 indicated functions for this water channel in the secretion of bile and pancreatic juice, and the secretion or absorption of water in the colon and jejunum, and the maturation or liberation of spermatogenic cells in the testis.

Aquaporins: Their role in cholestatic liver disease

“…We and others have recently shown that rat hepatocytes express mRNA and protein for AQP0 [16] , AQP8 [16][17][18][19][20] , AQP9 [16,21,22] and AQP11 [6] . In addition, other cells of the hepatobiliary tract such as cholangiocytes, gallbladder epithelia and peribiliary vascular endothelia also express AQPs [23][24][25][26][27] .…”

Expression and Localization of Aquaporin Water Channels in Rat Hepatocytes

“…d-cAMP caused a significant increase in canalicular secretion, and this effect could be completely abrogated by both Me 2 SO and phloretin. *, p Ͻ 0.05. sion has also been demonstrated on the luminal side of seminiferous tubules, the apical membrane of pancreatic acinar cells, and in both absorptive epithelia of the colon and acinar cells of the salivary gland; whether AQP8 in these tissues is also regulated by a trafficking mechanism has not been explored (10,(33)(34)(35)(36).…”

Rat hepatocyte aquaporin-8 water channels are down-regulated in extrahepatic cholestasis

“…2 Rat hepatocytes express 3 members of the AQP family of proteins: AQP8, AQP9, and AQP0. [3][4][5][6][7][8][9][10] AQP8, which seems to be the most abundant AQP in hepatocytes, is predominantly localized in intracellular vesicles; its translocation to the canalicular plasma membrane is microtubule dependent and adenosine 3Ј,5Ј-cyclic monophosphate (cAMP) stimulated. 5,6,10 AQP9 resides exclusively on the sinusoidal plasma membranes of hepatocytes and thereby may facilitate the movement of water and certain small solutes.…”