Ultrastructural study of mouse renal glomeruli under various hemodynamic conditions by an "in vivo cryotechnique"

Three-dimensional ultrastructure of mouse renal glomeruli under various hemodynamic conditions was studied by scanning electron microscopy with an "in vivo cryotechnique" followed by freeze-substitution. These results were also compared with those of conventionally fixed glomeruli at different perfusion pressures. Some kidneys of anesthetized mice were directly frozen in vivo under normal blood flow condition. Others were frozen in the same way after ligation of the lower abdominal aorta or their heart arrest. The frozen specimens were routinely freeze-substituted, freeze-dried and ion-sputtered for SEM. For another conventional fixation method, some kidneys were perfused with glutaraldehyde at pressures of 150 cm or 250 cm water, and other renal cortical tissues were routinely immersion-fixed with glutaraldehyde. In freeze-substituted specimens with the in vivo cryotechnique, interdigitating foot processes of podocytes exhibited smooth surface contours with less shrinkage and their surfaces were arranged more tightly than those seen by the conventional fixation method. In the anesthetized mice, filtration slits between the foot processes were found to be narrow after the heart arrest, but they were wide under the normal blood flow condition. After the aorta ligation, the filtration slits became wider and the foot processes were more elongated. The ultrastructure of capillary loops in functioning renal glomeruli were revealed to be dynamically changing in the living state, depending on various hemodynamic conditions.