Characterization of an Na+-dependent glutamate/aspartate transporter from cultured Bergmann glia

The properties of a transport system specific for L-glutamate and L-aspartate activity expressed in Bergmann glia cells from chick cerebellum were examined. The uptake of D-[3H]aspartate was inhibited by the endogenous substrates L-aspartate (Ki = 62 microM) and L-glutamate (Ki = 60 microM). Of the identified uptake inhibitors, L-aspartate-beta-hydroxamate (Ki = 900 microM), L-alpha-aminoadipate (Ki = 2000 microM), 4,4'diisothiocyanatos-tilbene-2,2'-disulphonic acid (DIDS) (Ki = 1000 microM) and 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS) (Ki = 100 microM) inhibited D-[3H]aspartate uptake. Northern blot analysis, revealed the expression of a chick homologue of a the rat brain L-glutamate/L-aspartate transporter (GLAST). These data suggest that GLAST may be involved in the regulation of the parallel fibre-Purkinje cell synapse ensheathed by Bergmann glia.