Sphingomyelin is synthesized at the plasma membrane of oligodendrocytes and by purified myelin membranes: a study with fluorescent- and radio-labelled ceramide analogues

AbstractIn most cell types sphingomyelin is synthesized predominantly in the cis-medial compartments of the Golgi stacks whereas the contribution of the plasma membrane is much lower. The aim of this study was to assess the contribution of both compartments to the synthesis of sphingomyelin in myelinating cells. Therefore, oligodendrocytes from rat spinal cord were incubated in culture with fluorescently- or radiolabelled ceramides, and the effects of a block in the vesicular flow (monensin, brefeldin A, low temperature) on surface synthesis of sphingomyelin were evaluated. The results indicate that ≈50% of the sphingomyelin synthase is present at the plasma and myelin membranes of oligodendrocytes

Uptake and metabolism of fluorescent ceramide analogs by rat oligodendrocytes in culture

AbstractWe studied the metabolism of sphingolipids by oligodendrocytes derived from rat spinal cord by providing lipid vesicles with either N-lissamine-rhodaminyl-ceramide (LRh-Cer) or N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-ceramide (NBD-Cer) to the cells cultured in a chemically-defined medium. With both probes them the fluorescent product turned out to be sphingomyelin (SM). Most or LRh-SM was not cell-associated but recovered from the culture medium, probably due to back-exchange to the lipid vesicles. The accumulation of LRh-SM, both in the cells and in the medium, was inhibited in the presence of monensin or brefeldin A, whereas the production of NBD-SM was much less affected by these Golgi perturbing drugs. With LRh-Cer as substrate, LRh-labelled fatty acid (FA), galactosyl- and sulfogalactosyl-ceramides (GalCer and SGalCer) were also formed. NBD-Cer, however, was metabolized to glucosylecramide (GlcCer) and GalCer but not to SGalCer or NBD-FA. These data demonstrate that chemical modifications of ceramide alter its metabolism in oligodendrocytes and that the metabolites of LRh-Cer reflect the glycolipid composition of myelin more closely than those of NBD-Cer