Ageing of mouse liver lysosomes

Summary Lysosomes in mouse liver parenchymal cells have been marked by intravenous injection of Thorotrast. They were subsequently followed in a time sequence from five hours up to sixteen weeks after injection. At two days after injection the majority of the lysosomes was heavily loaded with marker particles, while endocytosis was no longer observed. From six days after injection Thorotrast was partly accumulated in very large lysosomes (conglomerates) with mean diameters up to 2.5 m. As the time after injection advanced the Thorotrast content of the cells was reduced while most of the remaining marker substance became concentrated in the conglomerates. Many Thorotrast conglomerates were shown to contain acid phosphatase and some of them were able to fuse with functionally younger lysosomes which were marked with colloidal gold. Morphometric analysis showed an increase in the volume density of the dense body population between 0 and 2 days after injection, followed by a decrease between 2 and 11 days. The observed decrease is probably caused by exocytosis of the contents of Thorotrast containing lysosomes in bile capillaries.The author is highly indebted to Prof. Dr. J. James, Histological Laboratory, University of Amsterdam and Prof. Dr. W. Th. Daems, Laboratory for Electron Microscopy, University of Leiden for their stimulating advice and helpful criticism throughout this investigation. Advice on statistical analysis was given by Ir. J. J. Houtkooper, whose kind cooperation is gratefully acknowledged. Many thanks are due to the Application Laboratory of N. V. Philips at Eindhoven, The Netherlands, for facilities to make use of their equipment for X-ray microanalysis.