THE PARIETAL PODOCYTE - A STUDY OF THE VASCULAR POLE OF THE HUMAN GLOMERULUS

The vascular pole of the glomerulus is an important area of the nephron. The function of the juxtaglomerular apparatus (JGA) and the anatomical relationships of its tubular, glomerular and vascular components have been extensively studied. By comparison, the glomerular epithelium at the vascular pole has been neglected. In most species, simple squamous parietal cells are often separated from the podocytes on the capillary tuft by peripolar cells [1, 2]. In the human kidney, we found that, at the vascular pole, many Bowman's capsules were lined by cells which resembled podocytes. Since podocytes are highly differentiated for filtration, this finding would have important implications for the function of the glomerulus and its relationship with the underlying JGA and the surrounding interstitium. The aim of this study was to assess the extent of the parietal podocytic lining. We obtained human kidney tissue from the macroscopically and histologically normal parts of twelve kidneys surgically removed for renal cell carcinoma (8 cases) or transitional cell carcinoma of the renal pelvis (4 cases). The patients' ages ranged from 49 to 80 years. As before [1], the kidneys were perfusion-fixed and prepared for scanning electron microscopy (SEM). After critical point drying, the glomerular tufts were removed by microdissection and mounted on stubs. Tissue slices and glomerular tufts were gold-coated in a Polaron SEM sputter coater and viewed with a Jeol scanning electron microscope (JSM 6400). In each kidney, we examined a minimum of 20 vascular poles, at least 10 from superficial glomeruli and at least 10 from deep glomeruli. In six kidneys, we mapped the position in the renal cortex of each vascular pole, as before [1]. From these six kidneys, we also took 1 mm cube blocks from the superficial and juxtamedullary cortex of each kidney and processed them for transmission electron microscopy. Semithin sections, 2-mu-m thick, were examined by light microscopy to identify vascular poles, which were then ultrasectioned, stained with uranyl acetate and Reynold's lead citrate, and examined using a Philip's CM10 transmission electron microscope.