FORMATION OF FREE SPHINGOSINE AND CERAMIDE FROM EXOGENOUS GANGLIOSIDE GM1 BY CEREBELLAR GRANULE CELLS IN CULTURE

Cerebellar granule cells differentiated in culture were incubated with ganglioside [H-3-Sph]GM1 in order to have it inserted into the plasma membrane and metabolized. Among the formed metabolites radioactive spingosine and ceramide were identified. [H-3]Ceramide started to be measurable after 10 min of incubation (pulse), and [H-3]sphingosine after 15 min. Their concentrations increased with pulse time, and, after a 1-hour pulse, with chase time. After a 1-hour pulse with 2 x 10(-6) M [H-3-Sph]GM1 followed by a 4-hour chase, the amount of [H-3]sphingosine and [H-3]ceramide formed were 0.04 and 0.4 pmol/10(6) cells, respectively. Particularly the ability to produce sphingosine was higher in differentiated than in undifferentiated cells. It is concluded that ganglioside turnover contributes to the maintenance of the intracellular levels of free sphingosine and ceramide.