Decreased anionic sites in different portions of the basement membrane in aminonucleoside nephrosis

We induced aminonucleoside (AN) nephrosis in male Sprague-Dawley rats and evaluated the decreases in negative charge in the peripheral and proximal portions of the loop basement membrane and the basement membrane in the paramesangial area. Following intravenous injection of polyethyleneimine (PEI), the number of PEI granules per 0.1 micron 2 of the basement membrane, and those per 1 micron length of the lamina rara externa (LRE) and lamina rara interna (LRI) were counted in each portion under an electron microscope and compared with those in the control group. In the rats with AN nephrosis, the number of PEI granules per 0.1 micron 2 was significantly decreased in each portion of the basement membrane. However, the degree of decrease was similar among the 3 portions. The ratio of the numbers of granules in the proximal and paramesangial portions to that in the peripheral portion (peripheral:proximal:paramesangial) was 1:0.89:0.64 in the control group and 1:0.88:0.62 in the AN nephrosis group. Similar results were obtained for the numbers of PEI granules per 1 micron length of the LRE and LRI. These findings suggest that the negative charge is decreased in the loop basement membrane and paramesangial basement membrane in AN nephrosis, but the degree of decrease appears to be uniform.