Scanning electron microscope studies on rabbit renal glomerulus, with special reference to "podocytic membrane" of Elias and to pored domes on capillary endothelium.

Abstract

In their transmission electron microscope (TEM) study of the rabbit kidney, Elias et al. (1964, 1966) reported an occurrence of "podocytic membranes" which were attenuated parts of the body of the podocytes covering the processes and pedicels of podocytes and forming closed spaces, "subpodocytic lacunae" (Fig. 1, 2). In this scanning electron microscope (SEM) study, we demonstrate the three-dimensional structure of rabbit podocytes which largely confirms the Elias' diagram. However, the "podocytic membranes" are not as in Elias' view, attenuated portions of the body of the podocytes, but corresponds to their primary processes which are flattened into plates in this species. The "podocytic membranes" do not represent a second filtration barrier for the primary urine, which Elias proposed. On the glomerular endothelium, we found domed microprojections consisting of a pored cytoplasmic sheet not only in the attenuated portions of the endothelium or areolae fenestratae, but also in the nuclear portion of the endothelial cells. This hitherto unknown distribution of pored cytoplasm necessitates revision of the previous view which has interpreted the significance of the endothelial pores only from the aspect of substance transport through the capillary wall.