CYTOTOXIC EFFECTS OF KAINATE LIGANDS ON HEK CELL-LINES EXPRESSING RECOMBINANT KAINATE RECEPTORS

Exposure of neurons either for prolonged periods of time or to high co ncentrations of excitatory amino acids (EAA), such as glutamate, resul ts in neuronal death. Kainate also causes cell toxicity through the gl utamate receptors. However, it is unclear whether the kainate receptor itself mediates any of the toxic responses. In the present study, HEK cells expressing the GluR6 +/- KA2 receptor subunit(s) were studied f or their susceptibility to toxicity through the kainate receptor by ka inate ligands. The natural ligand, glutamate, did not result in toxici ty to the recombinant cell lines over that observed with the untransfe cted HEK cells, whereas kainate produced a 2-3-fold increase in LDH in both the HEK/GluR6 (ANOVA, P = 0.0001) and HEK/GluR6 + KA2 (ANOVA, P = 0.0002) cell lines following treatment with various dosages, but did not affect the HEK cells. Similar 2-3-fold increases in LDH activity were detected in both recombinant cell lines following treatment with 100 nM of SYM2081 ((2S,4R)-4-methylglutamic acid), a dose at which ago nistic activity is elicited. The rank order potencies for eliciting to xicity are consistent with the previously reported EC(50) values (SYM2 081 > kainate >>> glutamate). Surprisingly, the kainate antagonist, NB QX, was the most toxic of the compounds tested although it had an affi nity for the kainate receptor similar to glutamate. Treatment with as little as 10 nM elicited a dramatic increase in toxicity (6-10-fold) i n the recombinant cell lines. At 1 mu M, NBQX was significantly more t oxic (Fisher PLSD, P < 0.05) than any of the other compounds tested. T hus, it appears that cell toxicity can be mediated via kainate recepto r through two independent mechanisms: activation and blockage of the k ainate receptor.