Cultured cerebellar granule cells, but not astrocytes, produce an ester of ganglioside GD1b, presumably GD1b monolactone, from exogenous GD1b

Abstract

Granule cells and astrocytes from rat cerebellum were fed in culture with 2 microM ganglioside [Gal-3H]GD1b and then analysed for the presence of carboxyl esters of that ganglioside. Before extraction and purification of gangliosides, cells were treated with NaBH4 under conditions that would allow complete reductive cleavage of carboxyl ester linkages, [Gal-3H]GD1b monolactone and dilactone being used as reference esters of GD1b. These conditions, established by adding harvested cells (250 micrograms of protein) with 0.01-2 nmol of standard [Gal-3H]GD1b monolactone or dilactone and [Gal-3H]GD1b-1ol or -2ol formed respectively, consisted of an NaBH4/cell protein ratio of 2:1 (w/w). Cerebellar granule cells, but not astrocytes, were able to produce a radioactive compound which was identified as GD1b-1ol. The formation of this compound increased with pulse (up to 4 h) and chase (up to 3 h) time after a 2 h pulse and also occurred when ganglioside endocytosis was blocked. It can be concluded that cerebellar granule cells are able to convert ganglioside GD1b into a carboxyl ester form, presumably GD1b monolactone. The natural occurrence of the same GD1b carboxyl ester in cerebellar granule cells was also demonstrated.