CHANGES IN INTRACELLULAR LOCATION OF SMALL PHAGOSOMES (MICROPINOCYTIC VESICLES) IN KIDNEY AND LIVER CELLS IN RELATION TO TIME AFTER INJECTION AND DOSE OF HORSERADISH PEROXIDASE

Abstract

The change in location of small phagosomes containing ingested horseradish peroxidase was investigated as a function of time after injection and dose. A spread of small phagosomes from the apical toward the basal poles was observed in the tubule cells of the kidney during the first 30 min after injection of peroxidase. In the proximal convoluted tubule cells, many small phagosomes were seen lying close to lysosomes, 15-30 min after protein injection, probably preceding fusion. Small phagosomes almost disappeared from the cells when their fusion with lysosomes was completed. In the distal tubule cells the, main transport of peroxidase occurred between the apical and basal regions, and only a minor part was transported to lysosomes. At greatly reduced loads, the cells of the proximal convoluted tubules and large collecting tubules continued to absorb the protein but peroxidase transport across the distal tubule cells was abolished. Phagosomes in glomerular epithelial cells were observed only when optimal conditions of fixation were applied. In the liver, most of the peroxidase accumulated in small phagosomes of lining endothelial cells. A new formation of lysosomes in these cells seemed to take place in relation to the digestion of peroxidase, suggesting the transformation of endothelial cells into Kupffer cells. Peroxidase was also transported across the liver cells and appeared in pericanalicular granules.