Astrocytes in cell culture incorporate GM1 ganglioside

Ganglioside GM1 3H-labelled at the terminal galactose was added to astrocyte cell cultures. GM1 incorporation was studied in the two typical forms of astrocytes in cell culture of flat and stellate morphology. There was a strong time- and concentration-dependent increase in GM1 incorporation for both cell types of astrocytes. The incorporation of GM1 into the stellate form increased continuously up to 48 h (maximum time studied), while the incorporation into the flat form reached a plateau at the same time. After 2 h of GM1 incubation additional gangliosides appeared; the latter resulted from the metabolism of the GM1 incorporated, indicating that astrocytes in cell culture can biosynthesize more complex gangliosides. To confirm that GM1 was indeed incorporated into astrocytes, two other different approaches were used. Astrocyte cells treated with 3H-GM1 were visualized using autoradiography. The specific marker for GM1, rhodamine-labelled choleratoxin, was used to detect the incorporated GM1 using fluorescence microsocpy. In both cases GM1 treated cells were intensely labelled. These observations indicate that exogenous GM1 ganglioside can also be integrated into the astrocyte membranes as occurs in other types of cells and membranes.