Coupling between giant axon Schwann cells in the squid

The nature of dye and electrical coupling between Schwann cells from the the squid giant axon, determined with microelectrodes, is described. Dye coupling (sensitive to dissection in sea water containing Ca 2+ ) and electrical coupling exists between Schwann cells. The electrical length constant of the Schwann-cell sheath is 25 µm and 100 µm along the axon circumference and long axis respectively. Schwann-cell membrane resistance is ~ 500 Ω cm 2 (corrected for coupling between cells). The coupling ratio between cells is 1:0.3, and is reduced by 2 mm octanol (1:0.03) and increased by 2 mm Ba 2+ (1:0.45). We conclude that as Schwann cells are weakly coupled and have a relatively low membrane resistance they are unlikely to be involved in the spatial buffering of axonally released K + .

The glial ensheathment of the soma and axon hillock of retinal ganglion cells

We have studied the glial investment of ganglion cells of the cat's retina, orienting the sections taken for electron microscopy so that the investment could be traced from the soma along the axon. The soma of each ganglion cell is covered by a close-fitting, continuous sheath formed by Müller cells. The axon hillock and the first part of the initial segment are invested by an extension of the somal sheath, and are thus enclosed in the same glial compartment as the soma. The initial segment extends a few microns past the Müller cell sheath; this last length of the initial segment is contacted by numerous processes of astrocytes, which converge on it in a pattern found also on nodes of the same axons, in the optic nerve. Beyond the initial segment, the intraretinal lengths of the axons are invested by both Müller cells and astrocytes, but the investment is strikingly incomplete. Large areas of axonal membrane have no glial cover, and lie close to other axonal membranes. The sequential arrangement of these distinct forms of glial wrapping of the soma, initial segment, and axon is described here for the first time. It is suggested that this pattern of glial investment controls the flow of current between dendrite and initial segment of the ganglion cell, defines the site of initiation of action spikes, and controls the formation of synapses on the soma and initial segment.

Expression of 20 KD homologous restriction factor of complement on myocardial cells: an immunohistochemical study using acetone-fixed and paraffin-embedded tissues.

Expression of 20 KD homologous restriction factor of complement (HRF20) (CD59) in normal human heart was immunohistochemically examined with monoclonal antibody (MAb) 1F5. HRF20 was clearly demonstrated on the cell surface membrane and intercalated discs of myocardial cells throughout the ventricular walls. Therefore, this factor may protect normal cardiomyocytes from complement deposition, which has been demonstrated on infarcted cardiomyocytes. Expression of HRF20 was also observed on endothelial cells of the endocardium and on blood vessels, including arteries, capillaries, and veins, and on the Schwann-cell sheath of peripheral nerve fibers. In the present study, we found that the epitopes of HRF20 were well preserved for immunohistochemistry even in acetone-fixed and paraffin-embedded tissues, as well as in frozen tissues that have been conventionally used for HRF20. This method using paraffin sections allows for easier staining and greater accuracy in histological examination.

Evidence for the glycoprotein nature of the cell sheath of Methanosaeta-like cells in the culture of Methanothrix soehngenii strain FE

The resilient of Methanothrix soehngenii strain FE was isolated. It contained carbohydrates (7%), mainly rhamnose, ribose, and fucose, which could be specifically liberated by alkaline hydrolysis or hydrazinolysis. Four oligosaccharide-containing fractions were separated; the two major fractions corresponded to large glycans composed of 15–30 residues. The whole sheath preparation was soluble in anhydrous hydrazine. A mild hydrazinolysis treatment led to a water-soluble glycoprotein fraction, which represented 60% of the starting material and contained 100% of the carbohydrates. These high molecular mass (> 500 kDa) glycoproteins were sensitive to pronase. Fast atom bombardment mass spectrometry analysis of the major glycopeptide fraction obtained after hydrogen fluoride treatment was in accordance with the presence of asparaginyl-rhamnose linkages on a Asn-X-Ser glycosylation site. This type of glycosidic linkage has been described previously in the surface layer of Bacillus stearothermophilus. Key words: Methanothrix soehngenii, Methanosaeta concilii, archaebacteria, bacterial glycoprotein, proteic sheath, asparaginyl-rhamnose.