A new freeze-drying device for platinum replica studies of cell surface and cytoskeleton: an example using immunogold-labeled human erythrocytes.

We designed and built a freeze-drying device that ensures the protection of the specimens against contaminants during mounting on the cold stage of the freeze-fracture machine, transferring into the vacuum chamber and deep etching. The device consists of a copper cap that covers the specimen and a thermal connection that ensures thermal transfer between the microtome arm and the copper cap. This device was used to study the ultrastructural features of the erythrocyte membrane skeleton and the immunocytochemical localization of spectrin in an "in situ" approach, by freeze drying and platinum rotary shadowing. Human erythrocytes adhered to polylysine-coated coverslips and were broken by a stream of buffer that mimics the intracellular ionic environment ("inside buffer"). The samples were prefixed in periodate-lysine-paraformaldehyde fixative, labeled with antispectrin 5-nm gold particles, fixed in glutaraldehyde, mordanted in tannic acid, postfixed in OsO4, repeatedly washed in water, rinsed quickly in 30% ethanol, freeze-dried, and rotary-shadowed. Electron microscopic examination of the replicas revealed the skeletal network on the inner surface of the erythrocyte membrane. Immunocytochemical labeling proved that spectrin represents a fibrillar component of the network. Our data confirm the speculative model of the molecular organization of the erythrocyte skeleton, based on studies on in vitro association of proteic constituents. Both the technique and the device developed by us may lead to a deeper understanding of the spatial organization of the cytoskeletal network of more complex cell types.