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. 1986 Mar;6(1):43–53. doi: 10.1007/BF00742975

Ultrastructure of the Squid Axon Membrane as Revealed by Freeze-Fracture Electron Microscopy

Donald C Chang 1,2, Ichiji Tasaki 3
PMCID: PMC11567218  PMID: 3719619

Abstract

  1. The structure of the axolemma of the squid giant axon was studied by freeze-fracture electron microscopy.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. On the basis of existing physiological and biochemical information about the estimated size and density of the so-called sodium-channel proteins, we suspect that some of the IMP at the P-face of the axolemma, especially those with diameters between 9 and 11 nm, may be associated with the intramembrane component of the sodium channels.

Key words: ultrastructure; nerve, squid axon; freeze-fracture; electron microscopy; excitable membrane; sodium channel

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