IMMUNOHISTOCHEMICAL LOCALIZATION OF FACILITATED-DIFFUSION GLUCOSE TRANSPORTERS IN RAT PANCREATIC-ISLETS

The subcellular localization of five isoforms of facilitated-diffusion glucose transporters (GLUTs), from GLUT1 to GLUT5, in rat pancreatic islets was studied by immunohistochemistry using rabbit polyclonal ant isera against mouse or rat GLUT peptides. Animals were perfusion-fixed with phosphate-buffered 4% paraformaldehyde and the pancreases were r emoved. Some specimens were embedded in paraffin, serially sectioned, and immunostained for glucagon, insulin, somatostatin, and the GLUTs f or light microscopic observation. Others were prepared for immunoelect ron microscopy by the post-embedding method. By these methods, GLUT2 i mmunostaining was observed on the lateral membranes of pancreatic beta -cells, whereas GLUT3 immunoreaction was predominantly localized in th e cytoplasm of beta-cells and was not found in alpha-cells. In contras t, GLUT5 immunostaining was preferentially localized in the cytoplasm of alpha-cells compared to that of beta-cells. However, GLUT1 and GLUT 4 were either barely or not at all detectable in any cells. These resu lts suggest that rat islets take up glucose by at least three differen t processes and that blood glucose levels could be modulated different ially by: a high Km glucose transporter, GLUT2, in beta-cells; by a lo w Km glucose transporter, GLUT3, in beta-cells; and by a low Km glucos e transporter, GLUT5, in alpha-cells.