SPHINGOMYELIN IS SYNTHESIZED AT THE PLASMA-MEMBRANE OF OLIGODENDROCYTES AND BY PURIFIED MYELIN MEMBRANES - A STUDY WITH FLUORESCENT AND RADIOLABELED CERAMIDE ANALOGS

In 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 approximate to 50% of the sphingomyelin synthase is present at the plasma and myelin membranes of oligodendrocytes.