Inner blood-retinal barrier GLUT1 in long-term diabetic rats: an immunogold electron microscopic study.

PURPOSE The GLUT1 glucose transporter mediates glucose entry into the endothelial cells of the inner blood-retinal barrier (BRB). In many cell types, exposure to high glucose concentrations or diabetes downregulates GLUT1. To determine whether long-standing diabetes alters the expression and distribution of inner BRB GLUT1, changes in immunoreactive retinal endothelial cell GLUT1 were studied in Goto-Kakizaki (GK) rats, an animal model of type 2 diabetes. METHODS Immunogold staining for GLUT1 was performed on ultrathin sections of retinal specimens obtained from 1-year-old GK rats and age-matched Wistar controls. Retinal capillary endothelial cells were visualized by transmission electron microscopy, and GLUT1 immunogold was quantified on the luminal and abluminal membranes of endothelial cells from digital microphotographs of individual vessels by computer. RESULTS Forty-one microvessels from six diabetic rats and 43 microvessels from six nondiabetic Wistar control rats were analyzed. Densitometric quantification revealed an asymmetry of GLUT1 distribution between luminal and abluminal membranes of both diabetic and nondiabetic rats, with a luminal-to-abluminal ratio of approximately 1 to 3. The distribution pattern and density of retinal endothelial GLUT1 immunoreactivity were not significantly different between the diabetic and control rats. CONCLUSIONS As determined by GLUT1 immunogold distribution, there is no compensatory downregulation of GLUT1 on the inner BRB in an animal model of long-standing diabetes.