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BR Smith, R Varadaraj, A Krushinski, P Donaldson, R Mathias, J Kistler; Glucose Transport In the Lens . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4646.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Transport of glucose in the lens is mediated by members of the facilitative and Na+-dependent glucose transporters. We have investigated which isoforms are expressed in the rat lens, their spatial distribution, their functionality, and their regulation in the diabetic lens. Methods:Glucose uptake was measured using fibre cell membrane vesicles and fluorescently labelled glucose (2-NBDG). Transporter isoforms were identified by RT-PCR, and Northern analysis was used to determine transcript levels. Western blotting and immunocytochemistry, using commercially available antibodies, were employed to verify the presence and spatial distribution of glucose transporter proteins in normal and diabetic lenses. Quantitative RT-PCR and Northern analysis was used to determine changes in the levels of glucose transporter transcripts in the diabetic lens. Results:Transcripts for GLUT1, 3 and 5 and SGLT1 and 2 were detected in the rat lens. GLUT1, SGLT1 and SGLT2 were expressed in the epithelium, while GLUT3, GLUT5 and SGLT1 were present in the fibre cells. Western blotting confirmed the presence of glucose transporter proteins, and immunostaining of lens sections confirmed their differential spatial distribution. Kinetics measurements of glucose uptake indicated that GLUT3 is functional, and inhibitor studies show that most likely SGLT1 also contributes to glucose transport in the fibre cells. GLUT3 was up-regulated in the streptozotocin-induced diabetic rat lens and also in a hyperglycaemic lens culture model. The tissue damage phenotypes of the lenses from the diabetic rat and isolated lenses incubated in high glucose were identical. Conclusion:GLUT3 is the predominant transcript in lens fibre cells, and the transporter protein is functional. SGLT1 has also been detected and is likely to be functional. In the diabetic lens, GLUT3 is up-regulated and seems to contribute to the osmotic damage in the cortex. This is supported by the overlap of the regions of increased transporter expression and formation of tissue lesions. A similar situation was also observed in the hyperglycaemic lens organ culture model. This now provides the advantage that the in vitro model may be used to investigate novel ways to prevent cataractogenesis.
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