Glutamatergic excitation and GABA release from a transplantable cell line.

The cell line M213-2O CL-4 was derived from cell line M213-2O and further modified to express human glutamate decarboxylase (hGAD-67), the enzyme that synthesizes GABA. Brain transplants of this cell line in animal models of epilepsy have been shown to modulate seizures. However, the mechanisms that underlie such actions are unknown. The purpose of the present study was to characterize this cell line and its responsiveness to several depolarizing conditions, in order to better understand how these cells exert their effects. Intracellular GABA levels were 34-fold higher and GAD activity was 16-fold higher in clone M213-2O CL-4 than in M213-2O. Both cell lines could take up [³H]GABA in vitro, and this uptake was prevented by nipecotic acid. By combining GABA release measurements and calcium imaging in vitro, we found that high extracellular K(+), zero Mg(2+), or glutamate activated M213-2O CL-4 cells and resulted in GABA release. The response to glutamate appeared to be mediated by AMPA/NMDA-like receptors. High KCl-induced GABA release was prevented when a Ca(2+)-free Krebs solution was used, suggesting an exocytotic-like mechanism. These results indicate that the cell line M213-2O CL-4 synthesizes, releases, and takes up GABA in vitro, and can be activated by depolarizing stimuli.