CULTURED CEREBELLAR GRANULE CELLS, BUT NOT ASTROCYTES, PRODUCE AN ESTER OF GANGLIOSIDE G(D1B), PRESUMABLY G(D1B) MONOLACTONE, FROM EXOGENOUS G(D1B)

Granule cells and astrocytes from rat cerebellum were fed in culture with 2 mu M ganglioside [Gal-H-3]G(D1b) 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-H-3]G(D1b) monolactone and dilactone being used as reference esters of G(D1b). These conditions, established by adding harvested cells (250 mu g of protein) with 0.01-2 nmol of standard [Gal-H-3]G(D1b) monolactone or dilactone and [Gal-H-3]G(D1b)-1ol or -2o1 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 G(D1b)-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 G(D1b) into a carboxyl ester form, presumably G(D1b) monolactone. The natural occurrence of the same G(D1b) carboxyl ester in cerebellar granule cells was also demonstrated.