On the lysosomal function of juxtaglomerular granules

Abstract

The presence of acid phosphatase, β-glucuronidase and aryl sulfatase in juxtaglomerular cell granules (JGG) as well as the uptake and concentration of certain low molecular weight dyes by these granules have repeatedly suggested that they are akin to lysosomes. In the present experiments, rats were injected with three substances of widely different molecular weight and physicochemical properties - sucrose, iron sorbitol-citric acid complex (Jectofer) and horseradish peroxidase - that are well known to selectively concentrate in renal tubular cell lysosomes. None of these substances was found to enter the JGG to any significant degree, although both sucrose and Jectofer were evident in juxtaglomerular cells. Contrary to previous reports, thorium dioxide (Thorotrast) particles were not detected in the JGG after parenteral injection. These results indicate that JGG do not possess any significant lysosomal function and raise the question of the role of hydrolytic enzymes in the physiology of these granules.