Regulation of the Na+-dependent glutamate/aspartate transporter in rodent cerebellar astrocytes.

The regulation of the Na+-dependent glutamate/aspartate transporter system GLAST expressed in rat and mouse cerebellar and cortical astrocytic cultures was examined. Pretreatment of the cerebellar cells with L-glutamate and 12-O-tetradecanoyl-phorbol-13-acetate (TPA), a known Ca2+/diacylglicerol-dependent protein kinase (PKC) activator, produced a decrease in [3H]-D-aspartate uptake. This reduction was dose- and time-dependent and sensitive to PKC inhibitors. Furthermore, the L-glutamate-dependent [3H]-D-aspartate uptake decrease is a non-receptor dependent process, because neither of the agonists or antagonists were effective in mimicking or reverting the effect. Interestingly, transportable substrates could reproduce the L-glutamate effect. In sharp contrast, in cortical astrocytes, both L-glutamate and TPA pre-exposure result in an augmentation of the [3H]-D-aspartate uptake. These findings suggest that the Na+-dependent glutamate uptake GLAST undergoes a region-specific regulation.