Fig. 3. The effects of opioids on the dose-response relationships of the ε2/ζ1 channel for L-glutamate and glycine. ( A ) Dose–response relationships of the ε2/ζ1 channel for L-glutamate in the presence of 10 μM glycine and those for glycine in the presence of 10 μM L-glutamate before and during perfusion of 300 μM meperidine. The measured current responses were normalized to the control current responses to 10 μM L-glutamate plus 10 μM glycine. The EC50values (μM) of the ε2/ζ1 channel for L-glutamate before and during perfusion of 300 μM meperidine were 1.03 ± 0.02 and 1.04 ± 0.04, respectively, and the Hill coefficient values for those were 1.53 ± 0.04 and 1.62 ± 0.10, respectively (n = 6 or 7). The EC50values (μM) of the ε2/ζ1 channel for glycine before and during perfusion of 300 μM meperidine were 0.29 ± 0.01 and 0.29 ± 0.01, respectively, and the Hill coefficient values for those were 1.42 ± 0.05 and 1.56 ± 0.07, respectively (n = 6 or 7). ( B ) Dose–response relationships of the ε2/ζ1 channel for L-glutamate in the presence of 10 μM glycine and those for glycine in the presence of 10 μM L-glutamate before and during perfusion of 300 μM morphine. The EC50values (μM) of the ε2/ζ1 channel for L-glutamate and glycine during perfusion of 300 μM morphine were 1.05 ± 0.03 and 0.26 ± 0.02, respectively, and the Hill coefficient values for those were 1.38 ± 0.05 and 1.44 ± 0.09, respectively (n = 6 or 7).