QUANTITATION AND IMMUNOLOCALIZATION OF GLUCOSE TRANSPORTERS IN THE HUMAN PLACENTA

The subcellular distributions of the mammalian passive glucose transpo rter isoforms GLUT1, GLUT3 and GLUT4, in the human placenta, were inv estigated using isoform-specific anti-peptide antibodies. On western b lots of both basal and brush-bolder plasma membranes isolated from the syncytiotrophoblast, antibodies specific for GLUT1 labelled a broad b and (apparent Mr 55 000) that co-migrated with the human erythrocyte G LUT1 glucose transporter. In contrast, no labelling was detectable whe n blots mere probed with antibodies specific for the GLUT3 or GLUT4 is oforms. Densitometric analysis of blots showed that GLUT1 accounts for approximately 90 and 65 per cent of the D-glucose-sensitive cytochala sin B binding sites present in brush-border and basal membranes, respe ctively. Confocal immunofluorescence microscopy of fixed placental tis sue showed that GLUT1 is abundant at both maternal- and fetal-facing s urfaces of the syncytiotrophoblast whereas it was undetectable at the fetal capillary endothelium. In parallel experiments, no staining by a ntibodies against either the GLUT3 or the GLUT4 isoforms mns detected in placental tissue. These results indicate that GLUT1 is the major is oform responsible for glucose transfer from mother to fetus. The absen ce of GLUT4 is consistent with the lack of insulin-sensitive glucose t ransport across the placenta.