Pharmacological characterization of a GluR6 kainate receptor in cultured hippocampal neurons

We have examined the pharmacology of kainate receptors in cultured hippocam pal neurons (6-8 days in vitro (DIV)) from embryonic rats (E17). Cultured n eurons were pre-treated with concanavalin A to remove kainate receptor dese nsitization and whole-cell voltage clamp electrophysiology employed to reco rd inward currents in response to glutamatergic agonists and antagonists. N -methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepr oprionic acid (AMPA) receptor responses were blocked using MK801 (3 mu M) a nd the 2,3-benzodiazepine, LY300168 (GYKI53655, 50 mu M), respectively. Inw ard currents were recorded in hippocampal neurons upon application of kaina te and the 2S,4R isomer of 4-methyl glutamic acid (SYM2081) with EC50 value s of 3.4 +/- 0.4 mu M and 1.6 +/- 0.5 mu M, respectively (n = 6 cells). The GluR5 selective agonists, LY339434 (100 mu M) and (RS)-2-amino-3-(3-hydrox y-5-tert-butyl-4-isoxazolyl) propionic acid (ATPA) (100 mu M), did not evok e detectable inward currents in any cell responding to kainate. LY293558 an d the selective GluR5 antagonist, LY382884, had weak antagonist effects on responses evoked by either kainate or (2S,4R)-4-methyl glutamate (IC50 > 30 0 mu M). The quinoxalinedione, 2,3-dihyro-6-nitro-7-sulfamoyl-benzo(f)quino xaline (NBQX), blocked both kainate and (2S,4R)-4-methyl glutamate-activate d currents at much lower concentrations (IC50 approximately 10 mu M). These results provide pharmacological evidence that ion channels comprised of Gl uR6 kainate receptor subunits mediate kainate receptor responses in hippoca mpal neurons cultured 6-8 DIV. (C) 1999 Elsevier Science B.V. All rights re served.