GYKI53655 hydrochloride is an α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) antagonist. IC50 & Target: AMPA^{[1] In Vitro: GYKI53655 hydrochloride (LY300168) inhibits α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) (10 μM)-induced responses with IC₅₀ value of 5.9±0.1 μM. GYKI53655 hydrochloride inhibits AMPA (10 μM) responses in recombinant G1uR4 expressing HEK293 cells with IC₅₀ value of 4.6±0.4 μM. Using 3 μM cyclothiazide the inhibition produced by GYKI53655 hydrochloride is 79±2% (n=4 cells). GYKI53655 hydrochloride produces only small inhibitions of kainate-induced currents at 30 μM and inhibits kainate-induced currents at a concentration of 100 μM by 12±2 (n=4) and 18±4 (n=4), respectively. GYKI53655 hydrochloride inhibits AMPA receptor-mediated responses in cerebella Purkinje neurons with an IC₅₀ value of 1.5±0.1 μM[1]. In Vivo: GYKI53655 hydrochloride (4 mg/kg) is found to have a short-lasting depressant effect on neuronal responses to iontophoretic α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), with a half-recovery time of approximately 7 min. GYKI53655 hydrochloride (4 and 8 mg/kg) substantially depresses or completely abolishes AMPA responses. Results demonstrate the dose-dependence of GYKI53655 hydrochloride (2 to 8 mg/kg) in depressing responses to AMPA. At the highest doses tested, GYKI53655 hydrochloride reduces AMPA responses to a comparable degree[2]. Tonic fit and death are completely prevented by GYKI53655 hydrochloride at dose over 5.0 mg/kg. The ED₅₀ value of GYKI53655 hydrochloride is 2.2 mg/kg i.p. The maximal effects of GYKI53655 hydrochloride lasts 3 h then the exit inhibition effect of GYKI53655 hydrochloride falls to 20% 1 h later[3].}