RELEASE OF [H-3] D-ASPARTATE FROM PRIMARY ASTROCYTE CULTURES IN RESPONSE TO RAISED EXTERNAL POTASSIUM

There are significant Ca2+-independent increases in extracellular glut amate and aspartate during various CNS insults such as ischemia and an oxia. However, the cellular sources of such presumed nonvesicular exci tatory amino acid (EAA) release have not been established, To further explore potential mechanisms and sites for EAA release, we studied the release of preloaded [H-3]-D-aspartate from primary cultured astrocyt es prepared from the cerebral cortices of rat pups. Two phases of rele ase were seen in response to raised KCI. The first phase was small and transient, and the second phase was slower and increased progressivel y. The initial phase of [H-3]-D-aspartate release was greatly enhanced by ouabain pretreatment and was inhibited when astrocytes were preexp osed to the EAA transport inhibitor threo-hydroxy beta-aspartic acid ( THBA). Neither of these manipulations affected the second release comp onent. The second phase of release was inhibited by an anion channel b locker, L-644,711, which is known to inhibit hypotonic swelling-induce d release of EAA, Ouabain also resulted in the first phase of release occurring at lower [K+](o). Omission of Ca2+ had no effect on either p hase of [H-3]-D-aspartate release. These results support the hypothesi s that the first component of release in cultured astrocytes is a reve rsal of the glutamate transporter, and the second component is a resul t of high KCI-induced swelling. Because marked increases in [K+](o) ar e well established in CNS pathologies such as ischemia, such release m ay represent a significant source for the increased extracellular EAAs seen in such conditions.