Effect of point mutations within the BETA 7,8 domain of GluR1 on modulation by cyclothiazide. a, An alignment of GluR1 and GluR6 sequences within the BETA 7,8 domain showing that there are 10 identical (dashes) and 4 nonidentical residues. Each of the divergent residues was mutated in GluR1 to the side chain found in GluR6 and analyzed for function and sensitivity to cyclothiazide. b, Individual, whole-cell responses in transiently transfected HEK293 cells rapidly perfused with 100 msec pulses of 10 mm glutamate in control conditions (hairline) or in the presence of 100 μmCTZ (bold line). The time constant for desensitization of control responses is indicated with eachtrace. Calibration bars for current are shown for the control responses; responses in the presence of cyclothiazide were scaled to the peak amplitude of the control response. The mutation S₄₉₃T dramatically altered the ability of cyclothiazide to block desensitization, without altering control kinetics.c, Analysis of potentiation by cyclothiazide of point mutations, showing mean decay (I_STEADY-STATE/I_PEAK) after 100 msec in the presence of 100 μm cyclothiazide and 10 mm glutamate. Cyclothiazide failed to block desensitization only for GluR1-S₄₉₃T. Error bars represent SEM, and the number of cells studied is indicated inparenthesesabove eachcolumn. d, Mean time constants for desensitization of control responses for each point mutant. GluR1-I₅₀₀Y desensitization kinetics was significantly faster than that of wt GluR1 (*p = 0.00058).