IMMUNOHISTOCHEMICAL LOCALIZATION OF HEMOGLOBIN BINDING-SITES IN THE DISTAL TUBULE OF THE RAT-KIDNEY

Although it is well established that haemoglobin can be taken up by ki dney tubular epithelium, the exact mechanism of the process has not be en elucidated so far. We have undertaken a study to determine whether any specific binding sites for haemoglobin are present on the membrane s of renal tubular cells. Paraffin sections of rat kidney cortex were incubated with haemoglobin, and the bound molecules were detected by m eans of a combined avidin-peroxidase and ImmunoMax method. Haemoglobin binding sites were observed in the apical membrane of distal tubules. Binding occurred for both rat haemoglobin and swine and human haemogl obins, and the proteins could compete with each other. Competition exp eriments with other proteins showed that the binding is specific for h aemoglobin and that the net charge of the protein is not critical for the interaction. We failed to detect the binding sites in proximal tub ules, where most of the filtered proteins are reabsorbed. The role of the binding sites in the distal nephron is unclear. Our findings may b e essential for the further understanding of the pathomechanism of hae moglobin-induced acute renal failure. (C) 1998 Chapman & Hall.