Associated particle aggregates in juxtaparanodal axolemma and adaxonal Schwann cell membrane of rat peripheral nerve

Freeze-fracture observations have been made on unfixed cryoprotected, and glutaraldehyde-perfused and cryoprotected rat sciatic nerve. In the juxtaparanodal region of the internode, numerous particle clusters were observed on the axolemmal E face and rings of particles of uniform size on the P face of the adaxonal Schwann cell membrane. Both of these particle aggregates were concentrated in the internodal region immediately adjacent to the paranode (juxtaparanodal). The findings provide evidence for a close association between the two particle formations, suggesting a unitary structure forming links between the axolemma and Schwann cell membrane. Figures are given for the density distribution of these particles at the juxtaparanodal region. They were very rarely observed on membrane fracture faces of the general internodal regions. It is possible that these particle formations may represent potassium channels or that they could provide channels for other metabolic communication between the Schwann cell and the axon.