Figure 5. Exchange of any single region alone or in combination in GluR2i cannot produce the GluR2o kinetic response to allosteric regulation by LY404187. A, C, Whole-cell responses to 1.5 sec glutamate (1 mm) applications in the absence and presence of 1 μmLY404187 from HEK 293 cells expressing GluR2ii,o,i (A) or GluR2io,o,o (C) receptors. The responses of GluR2i or GluR2o are superimposed in light gray for comparison. B, D, Plot of the percentage change in potentiation in the presence of LY404187 for mutated receptors. B, Because the amino acid sequences of the GluR2 isoforms differ by one residue at the N-terminal border of region 3 (Ala796 in GluR2i and Ser796 in GluR2o; Fig. 3), an additional mutation of region 3 was made including this residue. Results showed that this mutation also did not alter the potentiation by LY40187 from that for GluR2i (GluR2ii,i,A796S,o, 188.9 ± 8.8%; n = 10; for other exchanges, see Results). D, Combination substitutions of regions failed to confer GluR2o potentiation (GluR2io,o,i, 150.1 ± 7.8%, n = 18; GluR2ii,o,o, 128.9 ± 5.2%, n = 6; GluR2io,i,o, 255.6 ± 20.2%, n = 7; for GluR2io,o,o, see Results). The percentage change in potentiation for GluR2i (R2i) and GluR2o (R2o) are indicated for comparison. Error bars represent mean ± SEM; n = 9-27 (F(5,77) = 53.22; p < 0.0001).