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L.M. Holm, T. Bek, S. Heegaard, S. Nielsen, J.U. Prause, H. Vorum, T. Zeuthen, S. Hamann; Localization and Function of Aquaporins 6–10 in Human and Rat Eye . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3317.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The eye is a fluid–filled organ and water transport is fundamental for ocular function. We have previously localized the aquaporin (AQP) water channels 1–5 in various ocular epithelia. Here we study the distribution of AQPs 6–10 and their transport ability. Methods: Localization of AQPs was determined by immunoblotting and high–resolution immunocytochemistry in human and rat ocular tissue. Transport properties were studied in Xenopus oocytes expressing rat AQPs by means of video–microscopy. We tested if the passive water permeability was associated with permeability to small hydrophilic molecules. The results were confirmed by radio–tracer experiments. Results: AQP6 was detected in the cytoplasm of: corneal epithelium, both ciliary epithelia, all retinal cell layers, lens epithelium, lens fiber cells and in the basolateral membrane of lacrimal gland acini. AQP7 was localized to plasma membranes of corneal epithelium and lens fiber cells. Cytoplasmic localization of AQP7 was found in ciliary non–pigmented epithelium, lens epithelium, retinal cell layers and lacrimal gland acini. AQP8 was detected in the cytoplasm of corneal epithelium, corneal endothelium, lens epithelium, all retinal cell layers, lacrimal gland and in the plasma membranes of lens fiber cells. AQP9 was observed intracellularly in ciliary non–pigmented epithelium and lens epithelium. Noteworthy, Müller cells exhibited distinct AQP9 labeling whereas other retinal cells did not label. AQP10 was prominent in corneal epithelial plasma membranes and in several retinal cell layers. Mercury chloride activated AQP6 supported urea, glycerol, acetamide, and formamide fluxes as shown by the respective mean reflection coefficients of 0.33, 0.65, 0.27, and 0.16. AQP7 was permeable to glycerol and formamide with mean reflection coefficients of 0.11 and 0.15. AQP8 was only permeable to formamide with a mean reflection coefficient of 0.20. AQP9 was selective to urea, glycerol, acetamide, and formamide, with mean reflection coefficients of 0.50, 0.48, 0.35, and 0.31. Conclusions: AQP6–10 are expressed in distinct ocular cell membranes. However, these aquaporins are predominantly localized to the cytoplasm indicating other roles than water transport. These transport characteristics are supported by our functional data indicating that substances other than water permeate the pores of these aquaporins.
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