title: Ultrastructure of the squid axon membrane as revealed by freeze-fracture electron microscopy.
abstract: The structure of the axolemma of the squid giant axon was studied by freeze-fracture electron microscopy. Three types of preparations were examined: intact axons, axons with their Schwann cell sheaths stripped off prior to freezing, and axons with their Schwann cell sheaths chemically detached but not mechanically removed. Because of a problem of cross-fracturing, the first two types of preparations revealed very few membrane faces of the axolemma. This cross-fracturing problem, however, was eliminated when we used a complementary replication method to fracture the third type of preparation. We found that the E-face of the axon membrane was smooth relative to the P-face, which showed many prominent intramembrane particles (IMP). The diameters of the typical IMP range from 6 to 15 nm. The P-face of the adjacent Schwann cells also showed many large IMP. The sizes and heights of the Schwann-cell IMP, however, appear to be more homogeneous than the P-face axolemma.
mesh_terms: D000818:Animals; D001369:Axons / Q000145:classification / Q000648:ultrastructure*; D002462:Cell Membrane / Q000648:ultrastructure; D049832:Decapodiformes; D005614:Freeze Fracturing; D008854:Microscopy, Electron; D012583:Schwann Cells / Q000648:ultrastructure