Effects of dextran on lysosomal ultrastructure and protein digestion in renal proximal tubule

The effects of dextran on renal ultrastructure and on the handling of protein by renal proximal tubules were evaluated in dextran-tolerant rats. In vivo and in vitro systems were studied by a combination of electron microscope and cell fractionation techniques. Dextran was demonstrated by electron microscopy in endocytic vacuoles and lysosomes ing a dextran-retaining fixative, and there was an increase in the number and size of the lysosomes in the proximal tubule cells using a dextran-retaining fixative, and there was an increase in the number and size of the lysosomes in dextran-treated rats. A lysosomal accumulation of dextran was also demonstrated when 3H-dextran T-80 was injected i.v. and the renal cortex analyzed by tissue fractionation. When radioactive lysozyme was injected into dextran-treated rats, there was less filtration of the protein in the kidneys than there was in the controls, but the rate of degradation of the labeled protein in slices prepared from the renal cortex and incubated in vitro was the same in the two groups. Electron microscope autoradiography revealed that radioactive lysozyme reabsorbed by the tubule cells had a similar location in both control- and dextran-treated rats. It is concluded that lysosomal protein catabolism is not altered by the presence of dextran despite pronounced ultrastructural changes in the lysosomal system. The decreased filtration of labeled protein after dextran infusion is probably related to the decreased GFR during and immediately after the dextran infusion.