Characterization of uptake and release processes for D- and L-aspartate in primary cultures of astrocytes and cerebellar granule cells.

The uptake of L- and D-aspartate was studied in astrocytes cultured from prefrontal cortex and in granule cells cultured from cerebellum. A high affinity uptake system for L- and D-aspartate was found in both cell types, and the two stereoisomers exhibited essentially the same Km- and Vmax-values in both astrocytes (L-aspartate: Km 77 microM; Vmax 11.8 nmol X min-1 X mg-1; D-aspartate: Km 83 microM; Vmax 14.0 nmol X min-1 X mg-1) and granule cells (L-aspartate: Km 32 microM; Vmax 2.8 nmol X min-1 X mg-1; D-aspartate: Km 26 microM; Vmax 3.0 nmol X min-1 X mg-1). To investigate whether L-glutamate, L-aspartate and D-aspartate use the same uptake system a detailed kinetic analysis was performed. The uptake kinetics of each one of the three amino acids was studied in the presence of the two other amino acids, and no essential differences between the uptake characteristics of the amino acids were found. In addition to the uptake studies the release of D-aspartate from cerebellar granule cells was investigated and compared with L-glutamate release. A Ca2+-dependent, K+-induced release was found for both amino acids.