Immunohistochemical localization of facilitated-diffusion glucose transporters in rat pancreatic islets

The subcellular localization of five isoforms of facillitated-diffusion glucose transporters (GLUTs), from GLUT1 to GLUT5, in rat pancreatic islets was studied by immunohistochemistry using rabbit polyclonal antisera against mouse or rat GLUT peptides. Animals were perfusion-fixed with phosphate-buffered 4% paraformaldehyde and the pancreases were removed. Some specimens were embedded in paraffin, serially sectioned, and immunostained for glucagon, insulin, somatostatin, and the GLUTs for light microscopic observation. Others were prepared for immunoelectron microscopy by the post-embedding method. By these methods, GLUT2 immunostaining was observed on the lateral membranes of pancreatic β-cells, whereas GLUT3 immunoreaction was predominatly localized in the cytoplasm to β-cells and was not found in α-cells. In contrast, GLUT5 immunostaining was preferentially localized in the cytoplasm of α-cells compared to that of β-cells. However, GLUT1 and GLUT4 were either barely or not at all detectable in any cells. These results suggest that rat islets take up glucose by at least three different processes and that blood glucose levels could be modulated differentially by: a high Km glucose transporter, GLUT2, in β-cells; by a low Km glucose transporter, GLUT3, in β-cells; and by a low Km glucose transporter, GLUT5, in α-cells.