In the initial stages of
aminonucleoside nephrosis, functional alterations in the glomerular basement membrane occur, as evidenced by the development of
proteinuria. However, it has not been possible to observe important ultrastructural modifications at the level of the basement membrane, probably because the changes are taking place at the molecular level. In this study, by the use of high-resolution electron microscopy, an attempt was made to evaluate such changes in rat glomerular basement membrane during acute
aminonucleoside nephrosis. As previously reported, in control animals the glomerular basement membrane is composed of a network of 4-nm-wide irregular anastomosing strands, referred to as "cords," which are known to contain a core filament of
type IV collagen surrounded by a "sheath" of other components, such as
laminin and
heparan sulfate proteoglycan (
HSPG). The most conspicuous ultrastructural alteration of the nephrotic glomerular basement membrane, recognizable only at high magnification, is that the cords were denuded leaving only the core filament through the loss of the sheath material. Thus, the cord network was transformed, with the progress of pathological conditions, into a network of fine filaments. On the other hand, abundance and distribution of
HSPG molecules known to be present in the form of 4.5- to 5-nm-wide ribbon-like "double tracks," were found to be similar in control and nephrotic tissues. Since
HSPG is one of the charge
proteins of the basement membrane, the little changes observed for
HSPG are difficult to interpret in view of reported decreases in basement membrane anionic sites in
nephrosis. In conclusion, the glomerular basement membrane in
aminonucleoside nephrosis loses its cord network components and replaces them with a more perforated network, which could be a cause for the increased permeability of this basement membrane.