Biochemical and immunocytochemical localization of the 'GLUT5 glucose transporter' in human skeletal muscle

Abstract

Using biochemical and immunocytochemical techniques, we have assessed both the protein expression and the cellular localization of the GLUT5 transporter in human skeletal muscle. Human muscle membranes, prepared by subcellular fractionation, were subjected to SDS/PAGE and Western-blot analyses using antiserum raised against a specific C-terminal amino acid sequence of the human GLUT5 transporter. GLUT5 was detected as a discrete 49 kDa protein band in a plasma-membrane-enriched fraction prepared from either soleus or gracilis muscle. In contrast, GLUT5 protein was not detectable to any significant extent in fractions which were devoid of muscle plasma membranes (mean GLUT5 abundance in intracellular fractions from three muscle preparations amounted to approximately 10% of that in the plasma-membrane-enriched fraction). Immunofluorescence studies using cryostat sections of human triceps muscle supported the biochemical observations and revealed that GLUT5 antibody selectivity labelled the plasma membrane of muscle cells. This immuno-labelling was significantly suppressed after tissue incubation with antiserum in the presence of a 14-amino-acid synthetic peptide corresponding to a specific C-terminus sequence of human GLUT5. These results indicate that human skeletal muscle expresses the GLUT5 transporter and that it is specifically localized to the plasma membrane, where it may participate in regulating hexose transfer across the sarcolemma.