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H. Oen, P. Cheng, H.C. Turner, O.A. Candia; Evidence for the Expression of Aquaporin 5 in the Mammalian Conjunctival Epithelium . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2913.
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© ARVO (1962-2015); The Authors (2016-present)
To demonstrate in the conjunctiva the presence of aquaporin type 5 (AQP5), a water channel homologue found in the apical membrane of several tissues including the cornea. Presently, there are no reports indicating as to which AQP might be expressed apically in the conjunctiva; only AQP3 has been identified in the lateral membranes of rat and human conjunctival epithelia. Because we had data from gene–expression microarray assays (Turner; ARVO 2004) indicating message for AQP5 in the human conjunctiva, tissue samples from human, as well as from rats and rabbits (given the ease of their procurement), were analyzed to confirm that the AQP5 protein was indeed expressed in mammalian conjunctivae.
Goat polyclonal IgG against AQP5 was purchased commercially and used in immunoblotting and immunohistochemical techniques to identify and localize the water channel in rat, rabbit and human epithelia.
Immunoblot analysis of rabbit bulbar–plus–palpebral plasma membrane fractions indicated specific binding of the anti–AQP5 antibody preparation to proteins of ≈27 and 45 kDa. The 27 kDa band represents the nonglycosylated form of the AQP5 monomer, while the 45 kDa band is presumed to be the glycosylated protein. These predominant bands were not observed in blots probed with IgG pretreated with blocking peptide supplied by the manufacturer. Indirect immunofluorescent labeling of frozen fixed sections from rat, rabbit and human conjunctivae revealed intense expression of AQP5 along the apical aspect of the epithelium of all species, as well as detectable lateral fluorescence emanating from between the more superficial epithelial cells.
Our results are consistent with the apical expression of AQP5 in the conjunctiva. Since others widely regard AQP5 as an apical homologue, with trafficking properties regulated by cAMP, the existence of this moiety in tandem with AQP3 in the conjunctiva may be necessary for transepithelial fluid transport. Moreover, AQP5 could serve as a potential target for pharmacological up–regulation that may enhance fluid secretion in individuals with dry–eye syndromes.
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