Comparative anatomy of the podocyte: A scanning electron microscopic study

The three-dimensional structure of the renal glomerular podocyte was comparatively analyzed with special reference to its cellular interdigitation. Kidneys of lampreys, carps, eels, xenopuses, bullfrogs, iguanas, rats, and rabbits were used as materials. Urinary and basal surfaces of podocytes were exposed by a conventional freeze-fracture method and by NaOH maceration, respectively, and subsequently examined by scanning electron microscopy. In accordance with previous reports, each podocyte consisted of a round cell body protruding into Bowman's space, four to six major processes embracing glomerular capillary, and numerous pedicels on both sides of the major processes. The podocyte pedicels exhibited uniform needle-like shapes, about 0.2 microm thick, interdigitated with those of adjoining cells along the entire length of the cell margins in all the animal species examined. This finding suggests that the fine pedicel interdigitation is a primary event in morphogenesis of the podocyte. The basal aspect of the glomerular epithelium was mosaicked with pedicels which were laid at various angles to the capillary axis, in favor of its possible role as a mechanical support of the capillary wall.