EXPRESSION OF HEMOPEXIN RECEPTORS BY CULTURED HUMAN CYTOTROPHOBLAST

The expression of cell-surface haemopexin (Hx) receptors on human cyto trophoblasts was assessed by using four different Hx species purified from plasma: human Hx isolated by wheatgerm-affinity chromatography, h uman Hx isolated by haem-agarose-affinity chromatography and rabbit an d rat Hx, also isolated by haem-agarose-affinity chromatography. About 3500-7000 high-affinity (K-d 0.34-0.85 nM) receptors per cell were me asured by Scatchard-type analysis at 4 Scatchard-type analysis at 4 de grees C using human (species obtained by both methods) or rabbit I-125 -labelled haem-Hx. Measured simultaneously, transferrin receptor numbe r and affinity were 40 000/cell and 0.83 nM respectively. In contrast with transferrin receptors, the number of Hx receptors did not increas e during 24 h in cytotrophoblast culture. Rat Hx showed no specific bi nding to human Hx receptors in cytotrophoblast cultures.