Structural and morphometric characteristics of the basement membrane of rabbit parietal podocytes induced by corticoids.

Abstract

This paper presents a structural and morphometric study of the basement membrane underlying the parietal epithelium of cysts developed in the rabbit kidney after a single postnatal injection of methylprednisolone acetate. This epithelium consists of podocyte-like cells named parietal podocytes. Our results show that the parietal podocytes synthesize their own basement membrane in vivo. However, the different laminae of this membrane present differences in structure and thickness when compared to the analogous layers of both the normal glomerular and parietal basement membranes. Differences between the different zones of the parietal podocytic basement membrane are also observed, depending upon the structure that surrounds the cyst (capillaries, interstitial cells or loose connective tissue). A lamina lucida, analogous to the lamina lucida interna of the glomerular basement membrane, is formed only in segments of the parietal podocytic basement membrane in close contact with endothelial or interstitial cells. The thickness of the lamina lucida externa of the parietal podocytic basement membrane appears regulated by the presence of interstitial cells and capillaries. In the zones in contact with capillaries, the lamina densa of the parietal prodocytic basement membrane appears thinner than in other segments. This fact, together with structural observations, suggests that the formation of a single basement membrane, interposed between the parietal podocytes and the endothelium, does not take place by fusion of the two basement membranes but by previous removal of the capillary basement membrane. In areas where the parietal podocytic basement membrane is in contact with loose connective tissue, a lamina fibroreticularis is observed. All these data indicate that the formation of the basement membrane by the parietal podocytes is influenced by nonpodocytic cells. Around the glomerular cysts, a tardy formation of capillaries is observed. Parietal podoytes can be hypothesized to synthesize an angiogenic factor that may be implicated in the process of angiogenesis.