Limits...
Functional gap junctions in the schwann cell myelin sheath.

Balice-Gordon RJ, Bone LJ, Scherer SS - J. Cell Biol. (1998)

Bottom Line: 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- 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA. rbaliceg@mail.med.upenn.edu

ABSTRACT
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- 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.

Show MeSH

Related in: MedlinePlus

High molecular mass compounds do not diffuse across  incisures. (A) Absence of a double line of dye staining 2 h after  pressure injection of 3,000-Da rhodamine-conjugated dextran.  (B) Subsequent confocal analysis of the same fiber did not reveal  a double line pattern anywhere in the z projection of the cell;  shown is a single confocal plane midway through the cell. Intensity profiles (marked by white arrowhead) illustrated at the bottom of each panel (scale, 0–255 intensity levels) confirm the absence of a doublet in any of the intensity peaks. In many cases,  dye appeared to pool in the outer collar of cytoplasm near incisures but did not fill them (for example, upper left-hand edge of  fiber above white arrowhead). Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2132877&req=5

Figure 6: High molecular mass compounds do not diffuse across incisures. (A) Absence of a double line of dye staining 2 h after pressure injection of 3,000-Da rhodamine-conjugated dextran. (B) Subsequent confocal analysis of the same fiber did not reveal a double line pattern anywhere in the z projection of the cell; shown is a single confocal plane midway through the cell. Intensity profiles (marked by white arrowhead) illustrated at the bottom of each panel (scale, 0–255 intensity levels) confirm the absence of a doublet in any of the intensity peaks. In many cases, dye appeared to pool in the outer collar of cytoplasm near incisures but did not fill them (for example, upper left-hand edge of fiber above white arrowhead). Bars, 10 μm.

Mentions: Since gap junctions have been reported to have a permeation limit at ∼1,000 Da (Bruzzone et al., 1996), we determined whether dyes of higher molecular mass would diffuse in a pattern similar to that observed with low molecular mass compounds. Pressure injection was used to inject large molecular mass dyes because iontophoretic injection was unreliable. Dye passage through the high resistance electrodes was difficult, and many injections were judged to have failed, either because dye did not diffuse beyond the perinuclear region or because the electrodes clogged during the injection (n = six out of nine injections from six mice). When 3,000-Da rhodamine-conjugated dextran was successfully injected into the perinuclear region (n = three fibers from three mice), dye spread longitudinally in a similar fashion to 5,6-carboxyfluorescein, except that fluorescence was not observed in the inner collar of Schwann cell cytoplasm. Even after allowing 1–4 h for additional diffusion (Fig. 6 A), dye remained confined to the outer collar of Schwann cell cytoplasm. Subsequent confocal analysis of the same fibers verified the absence of a double train track pattern of dye labeling (Fig. 6 B). Image analysis of intensity mapped along a line perpendicular to the long axis of injected fibers showed that no doublet in the intensity peaks was observed in any of the injected fibers (Fig. 6, A and B, bottom). Similar results were obtained in rats (data not shown) after injection of 3,000-Da fluorescein-conjugated dextran (n = three fibers from two rats) or 10,000-Da rhodamine-conjugated dextran (n = two fibers from one rat). Thus, low molecular mass, but not high molecular mass, compounds diffuse radially across the myelin sheath.


Functional gap junctions in the schwann cell myelin sheath.

Balice-Gordon RJ, Bone LJ, Scherer SS - J. Cell Biol. (1998)

High molecular mass compounds do not diffuse across  incisures. (A) Absence of a double line of dye staining 2 h after  pressure injection of 3,000-Da rhodamine-conjugated dextran.  (B) Subsequent confocal analysis of the same fiber did not reveal  a double line pattern anywhere in the z projection of the cell;  shown is a single confocal plane midway through the cell. Intensity profiles (marked by white arrowhead) illustrated at the bottom of each panel (scale, 0–255 intensity levels) confirm the absence of a doublet in any of the intensity peaks. In many cases,  dye appeared to pool in the outer collar of cytoplasm near incisures but did not fill them (for example, upper left-hand edge of  fiber above white arrowhead). Bars, 10 μm.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132877&req=5

Figure 6: High molecular mass compounds do not diffuse across incisures. (A) Absence of a double line of dye staining 2 h after pressure injection of 3,000-Da rhodamine-conjugated dextran. (B) Subsequent confocal analysis of the same fiber did not reveal a double line pattern anywhere in the z projection of the cell; shown is a single confocal plane midway through the cell. Intensity profiles (marked by white arrowhead) illustrated at the bottom of each panel (scale, 0–255 intensity levels) confirm the absence of a doublet in any of the intensity peaks. In many cases, dye appeared to pool in the outer collar of cytoplasm near incisures but did not fill them (for example, upper left-hand edge of fiber above white arrowhead). Bars, 10 μm.
Mentions: Since gap junctions have been reported to have a permeation limit at ∼1,000 Da (Bruzzone et al., 1996), we determined whether dyes of higher molecular mass would diffuse in a pattern similar to that observed with low molecular mass compounds. Pressure injection was used to inject large molecular mass dyes because iontophoretic injection was unreliable. Dye passage through the high resistance electrodes was difficult, and many injections were judged to have failed, either because dye did not diffuse beyond the perinuclear region or because the electrodes clogged during the injection (n = six out of nine injections from six mice). When 3,000-Da rhodamine-conjugated dextran was successfully injected into the perinuclear region (n = three fibers from three mice), dye spread longitudinally in a similar fashion to 5,6-carboxyfluorescein, except that fluorescence was not observed in the inner collar of Schwann cell cytoplasm. Even after allowing 1–4 h for additional diffusion (Fig. 6 A), dye remained confined to the outer collar of Schwann cell cytoplasm. Subsequent confocal analysis of the same fibers verified the absence of a double train track pattern of dye labeling (Fig. 6 B). Image analysis of intensity mapped along a line perpendicular to the long axis of injected fibers showed that no doublet in the intensity peaks was observed in any of the injected fibers (Fig. 6, A and B, bottom). Similar results were obtained in rats (data not shown) after injection of 3,000-Da fluorescein-conjugated dextran (n = three fibers from two rats) or 10,000-Da rhodamine-conjugated dextran (n = two fibers from one rat). Thus, low molecular mass, but not high molecular mass, compounds diffuse radially across the myelin sheath.

Bottom Line: 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- 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroscience, The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA. rbaliceg@mail.med.upenn.edu

ABSTRACT
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- 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.

Show MeSH
Related in: MedlinePlus