| Abstract: | This study was carried out to determine whether the ultrastructure of proximal tubules isolated and perfused in vitro was comparable to the ultrastructure of tubules fixed by perfusion in vivo. The kidneys of female white rabbits were either fixed by perfusion in vivo with glutaraldehyde (controls) or removed for dissection (experimentals) of proximal convoluted tubules and late proximal straight tubules. The isolated tubules were perfused in vitro with Krebs-Ringers bicarbonate solution for 1 hour after which the tubules were fixed with glutaraldehyde. The experimental tubules and the control tubules were processed for electron microscopy, compared qualitatively, and analyzed morphometrically to evaluate the volume densities and surface densities of different cell organelles and the cell membrane. Qualitatively, there were no differences in the appearance of cell organelles in experimental tubules and control tubules, except that cells in some experimental tubules accumulated small lipid droplets which were located close to mitochondria. Only a few quantitative changes were found, the most noteworthy being a 40% decreased surface density of the brush border in experimental proximal convoluted tubules and late proximal straight tubules. Damaged experimental tubules showed an increased number of vacuoles in the inverted microscope. In the electron microscope the vacuoles corresponded to swollen and disintegrated mitochondria and enlarged endocytic vacuoles. However, small degrees of tubular damage were not observable in the inverted microscope, as very small vacuoles could only be seen in the electron microscope. The results show that proximal tubules can be dissected and perfused in vitro for 1 hour without major ultrastructural changes. It should be emphasized that tubules showing an increased vacuolization in the inverted microscope may be damaged and, thus, not function optimally, and even if the tubules appear undamaged in the light microscope they may show signs of cellular degeneration in the electron microscope. |
