Characterisation of kainate receptor mediated whole-cell currents in rat cultured cerebellar granule cells.

Whole-cell voltage clamp recordings have been used to identify and characterise inward currents mediated by native kainate receptors in rat cultured cerebellar granule cells. While the selective AMPA receptor antagonist GYKI 53655 (50 microM) completely abolished inward currents evoked by AMPA (10-100 microM) in the presence of cyclothiazide (100 microM), kainate evoked currents in cells pretreated with concanavalin A (Con A) always showed a component (35-140 pA, n = 13) resistant to blockade. The majority (73+/-7%, n = 5) of GYKI 53655-resistant kainate-evoked inward currents remained in the presence of 100 microM AMPA. However, these currents were reversibly blocked by the competitive AMPA/kainate receptor antagonist NBQX (100 microM). (2S, 4R)-4-methylglutamate (SYM 2081, 10 microM) evoked inward currents in Con A treated cells (15-60 pA, n = 7), which were resistant to complete blockade by GYKI 53655 (50 microM) but antagonised by NBQX (100 microM). Kainate-evoked responses in the presence of GYKI 53655 (50 microM) had linear or slightly outwardly rectifying current-voltage (I-V) relationships in all cells examined (n = 5) and were resistant to blockade by Joro spider toxin (JsTx, 1 microM; n = 5). These results provide evidence that rat cultured cerebellar granule cells express functional kainate receptors made up of subunits which are edited at the Q/R site, and that SYM 2081 is an agonist at these native kainate receptors with a greater selectivity than kainate itself.