Characteristics of albumin binding to opossum kidney cells and identification of potential receptors

Albumin re-absorption in the kidney proximal tubule may be pathophysiological in disease. Opossum kidney (OK) cell monolayers were used to investigate the characteristics of [I-125]-labelled albumin binding at 4 degrees C. Two binding sites were identified, one with high affinity (K-D 154.8 +/- 7 mg/l) and low capacity, the other with low affinity (K-D 8300 +/- 1000 mg/l) and high capacity. Binding was sensitive to lectins Glycine max and Ulex europaeus I, but not other lectins, indicating involvement of a glycoprotein(s) in the binding process. Binding was also sensitive to a number of agents known to inhibit binding to scavenger receptors. [I-125]-Labelled albumin Ligand blotting of OK cell membrane proteins identified several albumin-binding proteins with identical lectin affinities to those proteins mediating albumin binding to OK cell monolayers. These results provide initial evidence of the identity of albumin receptors in kidney tubules, and suggest that they may be members of the family of scavenger receptors.