The effect of monensin on glycosphingolipid metabolism was reinvestigated. It was found that monensin increased the uptake of [3H]galactose by human fibroblasts, causing an enhanced metabolic labelling of glycosphingolipids. The preferential incorporation of radioactivity into ceramide monosaccharide in the presence of monensin was accompanied by an equally increased rate of degradation. However, using radiolabelled precursors of the ceramide moiety, a generally diminished uptake of radioactivity into all glycosphingolipids was observed under the influence of monensin, with the exception of mono- and di-hexosylceramide. The enhanced incorporation of radiolabel by these two glycolipids, as well as their increased cellular chemical content, may reflect early synthesis in a monensin-insensitive pre-Golgi compartment after disruption of the cellular Golgi transport system by monensin.
