Alterations in the distribution of plasma fibronectin and the ultrastructure of podocytes in the peripheral glomerular loops in nephrotic rats.

Glomerular distribution of rat plasma fibronectin was examined during the course of puromycin (PAN)- and daunomycin (DM)-induced nephrosis. In control animals, fibronectin was detected in the mesangial matrix and along the glomerular basement membrane (GBM), closely associated with the plasma membrane of glomerular cells. In peripheral loops, immunoprecipitates were preferentially distributed in the laminae rarae externa and interna. Fibronectin was densely precipitated in a glomerulosclerotic lesion induced by DM at 8 weeks after the injection. In peripheral loops, loss and reconstruction of epithelial foot processes occurred in PAN nephrosis but the change was accompanied by negligible perturbation of fibronectin distribution in the lamina rara externa. In contrast, a remarkable decrease of fibronectin was observed in DM nephrosis, unrelated to the presence or absence of foot processes. The decrease in immunoreactivity for fibronectin in the lamina rara externa seemed to have no association with podocyte attachment to or detachment from the GBM. Plasma fibronectin distributed in the lamina rara externa is not directly involved in the modification of podocyte configuration or podocyte attachment, although its spatial distribution may have some functional significance for preserving the ultrastructure of the GBM.