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J. Cell Biol.,
Volume 142, Number 4, August 24, 1998 1095-1104


* Department of Neuroscience and The Schwann cell myelin sheath is a multilamellar structure with distinct structural domains in
which different proteins are localized. Intracellular dye
injection and video microscopy were used to show that
functional gap junctions are present within the myelin
sheath that allow small molecules to diffuse between the adaxonal and perinuclear Schwann cell cytoplasm.
Gap junctions are localized to periodic interruptions in
the compact myelin called Schmidt-Lanterman incisures and to paranodes; these regions contain at least
one gap junction protein, connexin32 (Cx32). The radial diffusion of low molecular weight dyes across the
myelin sheath was not interrupted in myelinating
Schwann cells from cx32-null mice, indicating that
other connexins participate in forming gap junctions in
these cells. Owing to the unique geometry of myelinating Schwann cells, a gap junction-mediated radial pathway may be essential for rapid diffusion between the
adaxonal and perinuclear cytoplasm, since this radial
pathway is approximately one million times faster than
the circumferential pathway.
Department of Neurology, The University of Pennsylvania School of Medicine, Philadelphia,
Pennsylvania 19104-6074
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