Block of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) and kainate currents by GYKI 52466 [1-(4-aminophenyl)-4-methyl-7,8- methylenedioxy-5H-2,3-benzodiazepine], a noncompetitive non-N-methyl-D-aspartate (AMPA/kainate) receptor antagonist, and two 3-N-substituted 3,4-reduced GYKI 52466 analogs was assessed in whole cell voltage-clamp recordings from cultured rat hippocampal neurons. In addition, the activity of the analogs was determined in the maximal electroshock seizure test and for protection against kainate-induced seizures in mice. The analogs of GYKI 52466 tested were the 3-N-methylcarbamyl [GYKI 53655; 1-(4-aminophenyl)-3-methylcarbamyl-4- methyl-3,4-dihydro-7,8-methylenedioxy-5H-2,3-benzodiazepine] and the 3-N-acetyl [GYKI 53405; 1-(4-aminophenyl)-3-acetyl-4-methyl-3,4-dihydro-7,8-methylenedioxy-5H-2, 3- benzodiazepine]. GYKI 53655 produced a concentration-dependent inhibition of AMPA- and kainate-induced currents with IC50 values of 1.1 and 1.5 microM, respectively; the corresponding values for GYKI 53405 were 3.8 and 5.0 microM. As blockers of AMPA currents, the analogs were 8- and 2.3-fold, respectively, more potent than the parent GYKI 52466. Kinetic analyses indicated increased association rates for the two 3-N-substituted analogs (2.5-2.6 x 10(5) M-1 sec-1) compared with GYKI 52466 (1.6 x 10(5) M-1 sec-1). The dissociation rates of GYKI 52466, GYKI 53405 and GYKI 53655 were inversely correlated with increasing blocking potency (2.9, 1.7 and 0.6 sec-1, respectively). Thus, the increased affinity of the 3-N-substituted analogs relates to their increased binding and decreased unbinding rates.(ABSTRACT TRUNCATED AT 250 WORDS)