High-resolution scanning electron microscopy of frozen-hydrated and freeze-substituted kidney tissue

Inner surfaces and fracture faces of rabbit kidney tissue were investigated with high-resolution scanning electron microscopy using two different cryopreparation techniques: (i) for the observation of fracture faces, cryofixed tissue was fractured and coated in a cryopreparation chamber dedicated to SEM, vacuum transferred onto a cold stage and observed in the frozen-hydrated state; (ii) for the observation of inner surfaces of the nephron, water was removed after freezing and fracturing by freeze substitution and critical-point drying of the tissue. By both methods, macromolecular structures such as intramembranous particles on fracture faces and particles on inner surfaces were imaged. The latter method was used to investigate in more detail surface structures of cells in the cortical collecting duct. These studies revealed a heterogeneity of intercalated cells not described thus far.