title: Interaction between transcellular and paracellular water transport pathways through Aquaporin 5 and the tight junction complex.
abstract: To investigate potential physiological interactions between the transcellular and paracellular pathways of water transport, we asked whether targeted deletion of Aquaporin 5 (AQP5), the major transcellular water transporter in salivary acinar cells, affected paracellular transport of 4-kDa FITC-labeled dextran (FITC-D), which is transported through the paracellular but not the transcellular route. After i.v. injection of FITC-D into either AQP5 wild-type or AQP5-/- mice and saliva collection for fixed time intervals, we show that the relative amount of FITC-D transported in the saliva of AQP5-/- mice is half that in matched AQP5+/+ mice, indicating a 2-fold decrease in permeability of the paracellular barrier in mice lacking AQP5. We also found a significant difference in the proportion of transcellular vs. paracellular transport between male and female mice. Freeze-fracture electron microscopy revealed an increase in the number of tight junction strands of both AQP5+/+ and AQP5-/- male mice after pilocarpine stimulation but no change in strand number in female mice. Average acinar cell volume was increased by approximately 1.4-fold in glands from AQP5-/- mice, suggesting an alteration in the volume-sensing machinery of the cell. Western blots revealed that expression of Claudin-7, Claudin-3, and Occludin, critical proteins that regulate the permeability of the tight junction barrier, were significantly decreased in AQP5-/- compared with AQP5+/+ salivary glands. These findings reveal the existence of a gender-influenced molecular mechanism involving AQP5 that allows transcellular and paracellular routes of water transport to act in conjunction.
authors.affiliation: Department of Molecular Genetics, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0524, USA.
authors.forename: Jitesh D
authors.initials: JD
authors.lastname: Kawedia
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Nieman
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Boivin
authors.forename: James E
authors.initials: JE
authors.lastname: Melvin
authors.forename: Ken-Ichiro
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Hand
authors.forename: John N
authors.initials: JN
authors.lastname: Lorenz
authors.forename: Anil G
authors.initials: AG
authors.lastname: Menon
mesh_terms: D000818:Animals; D051402:Aquaporin 5 / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000502:physiology; D015153:Blotting, Western; D062465:Claudin-3; D057167:Claudins; D003911:Dextrans; D005260:Female; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046529:Microscopy, Electron, Transmission; D062793:Occludin; D012463:Saliva / Q000737:chemistry; D012469:Salivary Glands / Q000378:metabolism; D019108:Tight Junctions / Q000378:metabolism* / Q000648:ultrastructure; D014867:Water / Q000378:metabolism*
chemical_list: C496038:Aqp5 protein, mouse; D051402:Aquaporin 5; D062465:Claudin-3; D057167:Claudins; C568123:Cldn3 protein, mouse; C507360:Cldn7 protein, mouse; D003911:Dextrans; D008565:Membrane Proteins; D062793:Occludin; C568986:Ocln protein, mouse; C015219:fluorescein isothiocyanate dextran; D014867:Water; D016650:Fluorescein-5-isothiocyanate