Dynamic structure of glomerular capillary loop as revealed by an in vivo cryotechnique

Morphological studies using immersion or perfusion fixation methods do not reveal the ultrastructure of functioning kidneys with normal circulation. A simple apparatus was developed for freezing the kidneys in vivo without stopping the blood supply, and the ultrastructure of the glomerular capillary loops was examined under different haemodynamic conditions. Mouse kidneys were frozen under normal blood flow conditions; others were frozen in the same way after ligation of the abdominal aorta at a point caudal to the renal arteries. They were then processed for the freeze-substitution or deep-etching method. Good ultrastructural preservation was obtained within about 5 microM depth from the frozen tissue surface. Functioning glomeruli with normal blood flow possessed open capillary lumens, different shapes of foot processes and atypical basement membranes with low density. Moreover, heterogeneity in width between foot processes was identified on the replica membranes. Under the acute conditions used to increase blood supply into the kidneys, the spaces between the flat foot processes became more widely dilated and the basement membrane was seen to be three-layered. The ultrastructure of glomeruli in functioning kidneys has been demonstrated for the first time by this "in vivo cryotechnique."