Comparative analysis of sodium-dependent l-glutamate transport of synaptosomal and astroglial membrane vesicles from mouse cortex

Uptake of [³H]l-glutamate into membrane vesicles prepared from either mouse cortical astrocyte cultures or synaptosomes was found to be an electrogenic sodium- and potassium-dependent transport process with saturable uptake kinetics. Pharmacological differences were revealed by using a variety of substrate analogues. l-trans-PDC inhibited the synaptosomal glutamate transport 2-4-fold stronger than the astroglial uptake. The substrate analogues dl-threo-β-hydroxy-aspartate, dl-aspartate-β-hydroxamate, l-aspartate and d-aspartate inhibited glutamate transport of astroglial and neuronal membrane vesicles in a distinctive manner, whereas d-glutamate, quisqualate and dihydrokainate had no effect in either case. Immunoblotting and immunocytochemical labeling with antibodies against the rat brain glutamate transporter revealed the selective reaction of a band at about 75 kDa mol. wt. and a specific pattern of astrocyte immunostaining.