Kinetics of glomerular visceral epithelial cell phagocytosis

Abstract

The functions of the glomerular visceral epithelial cell include a) participation in the formation of the glomerular filtration barrier [1], b) the synthesis and maintenance of the glomerular basement membrane (GBM) [2], and c) the clearance of macromolecules from the glomerular filter. The latter characteristic has been repeatedly observed under a variety of experimental conditions. Morphologic evidence of the phagocytosis of filtered macromolecular dextran by epithelial cells has been demonstrated in normal glomeruli [3]. The epithelial cell uptake of significant amounts of larger tracers, such as ferritin, however, has been achieved only after rendering rats nephrotic, such as with administration of puromycin aminonucleoside [4]. Studies carried out in various experimental proteinuric states have also shown that some of the abnormally filtered albumin is taken up by the epithelial cells and sequestered in phagosomes within these cells [5]. Since macromolecular tracers are largely excluded from the lamina rara externa, the quantitation of epithelial cell phagocytic activity has hitherto not been accomplished.