Pharmacological characterization of glutamatergic agonists and antagonists at recombinant human homomeric and heteromeric kainate receptors in vitro

An increasing body of evidence suggests that native kainate receptors form ion channels from homemeric and heteromeric combinations of five receptor subunits: G1uR5. G1UR6, G1UR7. KA1 and KA2. We have examined the activity of agonists and antagonists at recombinant human kainate receptors expressed in HEK293 cells, Using both whole-cell electrophysiological recording and 96-well plate fluo-3 based calcium microfluorimetry (FLIPR). Both homomeric (GluR5 and G1uR6) and heteromeric (G1uR5/6. G]G1uR5/KA2 and G1uR6/KA2) receptors were examined. Hetomeric receptor assemblies showed electro-physiological and pharmacological profiles which were distinct from homomeric channels. several agonists. including AMPA, ATPA and (S)-5-iodowillardine, and antagonists, including gamma-D-glutamylaminomethylsul-phonic acid (GAMS) and the decahydroisoquinoline compounds LY293558, LY377770 and LY382884, were found to act at G1uR5-containing channels while having no effect at G1uR6 homomers. AMPA, ATPA and (S)-5-iodowillardiine did activate G1uR6/KA2 heteromers. but Only as partial agonists. Additionally. ATPA was shown to act as an antagonist at homomeric G1uR6 receptors at high concentrations (IC50 similar to 2 mM). Kynurenic acid was also found to differentiate between G1uR6 and G1uR6/KA2 receptors, antagonizing glutamate at G1uR6 (IC50 =0.4 mM), while having no effect at G1uR6/KA2 channels. The results of the current study provide a broad pharmacological characterization of both homomeric and heteromeric recombinant human kainate receptors. and identify which compounds are likely to be useful tools for studying these various receptor subtypes. (C) 2004 Elsevier Ltd. All rights reserved.