IMMUNOHISTOCHEMICAL LOCALIZATION OF GLUCOSE TRANSPORTERS AND INSULIN-RECEPTORS IN HUMAN FETAL MEMBRANES AT TERM

The localization has been investigated of the isoforms GLUT1, GLUT3 an d GLUT4 of glucose transporter proteins as well as of insulin receptor s. Fetal membranes (n = 10) were examined by immunohistochemical metho ds at the light and electron microscopic levels using mono- and polycl onal antibodies. In all amnion epithelial cells, GLUT1 and GLUT3 antib odies were bound to the apical membrane. Very rarely the GLUT1 antibod y also immunostained the basolateral membrane and reacted weakly with the endomembrane system and membranes of the lateral cell protrusions. Fibroblasts reacted with the antibodies against GLUT1, GLUT4 and insu lin receptor, whereas they were labelled only in one case with GLUT3 a ntibody. Cytotrophoblast cells were only stained with antibodies again st GLUT1 and GLUT3. Antibodies against GLUT4 only reacted with fibrobl asts in the membranes. On amnion epithelial cells, weak immunoreactivi ty with insulin receptor antibodies was detected only at the electron microscopic level. The data indicate: (1) GLUT1 is located on all cell s of the amnion, whereas GLUT3 is present in detectable amounts only o n amnion epithelial cells and cytotrophoblast; (2) GLUT1 and GLUT3 on amnion epithelial cells are predominantly located on the apical surfac e; (3) GLUT4 and insulin receptors are not regularly expressed. We sug gest that amnion epithelial cells cover their basal glucose requiremen ts from the amniotic fluid and not from the maternal circulation.