Ultrastructural changes in glomerular epithelial cells in acute puromycin aminonucleoside nephrosis: a study by high-resolution scanning electron microscopy.

Ultrastructural changes in the podocytes were studied during the development of, and recovery from, acute puromycin aminonucleoside (PAN) nephrosis using high-resolution scanning electron microscopy (hrSEM) and transmission electron microscopy (TEM). In the process of development of PAN nephrosis, four types of early structural changes were observed before total loss of foot processes: formation of cytoplasmic blebs, masking of filtration clefts, flattening of foot processes, and retraction of foot processes. The masking of filtration clefts visualized by hrSEM corresponded to the multiplication of slit diaphragms and adhesion of foot processes in the TEM findings, and preceded retraction of the foot processes. Changes of podocyte configuration were produced. Recovery from this change of podocyte configuration began as islands of podocyte interdigitation, and was proceeded by expansion of the islands. During recovery, the primary processes were re-established either by retraction or perforation of the thin cytoplasm after the formation of foot processes. We conclude that loss of foot processes begins with the masking of filtration clefts. Recovery from the change in podocyte configuration begins with the formation of new foot processes.