Modulation of kainate-activated currents by diazoxide and cyclothiazide analogues (IDRA) in cerebellar granule neurons

1. Patch-clamp technique was used in primary cultures of cerebellar granule neurons to study the modulation of the cyclothiazide analogue(IDRA21) and of the diazoxide derivative (IDRA 5) on KA-evoked currents. 2. The dose-response of kainic acid (KA) reveals an EC50=90 mu M and an Hil l coefficient of 1.3. IDRA 21 and cyclothiazide potentiate KA-evoked curren t in a dose-dependent way, being cyclothiazide more potent but less efficac ious than IDRA 21. Conversely IDRA 5 acts as a negative modulator of KA evo ked -current. 3. Application of IDRA 21 and cyclothiazide results in a current potentiati on of 125+/-18 % and 80 +/- 12 % respectively, while IDRA 5 decreases KA-cu rrent (-21+/-5 %). Coapplication of cyclothiazide and IDRA 21 produces a po tentiation of 110+/- 17 %, suggesting a competition of the two drugs for th e same site. 4. In the same experimental model we studied the ability of IDRA compounds of promoting toxicity through AMPA-receptor activation. Under basal conditi ons AMPA treatment (50 mu M for 1 hour) results in a negligible excitotoxic ity. 5. In contrast similar treatment with AMPA + IDRA 21 (1 mM) or + IDRA 5 (1 mM) or + cyclothiazide (100 mu M) induces citotoxicity. The neurotoxic dama ge induced by IDRA 21 and cyclothiazide is blocked by GYKI 53655 (50 mu M) and by NBQX (10 mu M). Interestingly GYKI and NBQX are ineffective in reduc ing IDRA 5 toxicity.