Salvage of catabolic products in ganglioside metabolism: A study on rat cerebellar granule cells in culture

Cerebellar granule cells in culture were subjected to a pulse (0.5-4 h)-chase (0-4 h) of 10(-6) M [H-3]ganglioside GM1 carrying the radioactive label at the level of NeuAc ([H-3-NeuAc]GM1), Sph ([H-3-Sph]GM1) or Gal ([H-3-Gal]GM1) and the formed [H-3]metabolites were determined, With all forms of [H-3]GM1, there was formation of [H-3]catabolites, including [H-3]H2O and [H-3]biosynthetic products obtained by recycling of [H-3]NeuAc, [H-3]Sph and [H-3]Gal released during intralysosomal ganglioside degradation (salvage processes), Much higher amounts of [H-3]H2O were produced from [H-3-Gal]GM1 than [H-3-Sph]GM1 and [H-3-NeuAc]GM1; conversely, more products from salvage processes (polysialogangliosides GD1a, GD1b, GT1b, O-acetylated GT1b, protein-bound radioactivity) were obtained with [H-3-NeuAc]GM1 than the two other forms of [H-3]GM1. Liberated [H-3]NeuAc produced 10-fold less tritiated water and 10-fold higher salvage products than [H-3]Gal. Using [H-3-NeuAc]GM1, granule cells appeared to metabolize 7.7% of membrane-incorporated exogenous GM1 per hour with a high degree of NeuAc recycling and the calculated metabolic half-life was 6.5 h.