A, sample trace showing only a small degree of blue-light potentiation of the response to 10 μm NMDA in the presence of 300 nm C2-NBD 3α5αP in the NR1a (C744A,C798A)-NR2B receptors expressed in HEK 293 cells. B, sample trace showing blue-light potentiation of wild-type NR1a-NR2B NMDA receptors. C, summary bar graph of blue-light potentiation of mutant receptors, wild-type receptors and 50 μm pregnenolone sulfate (Preg sulfate) potentiation of mutant receptors. Error bars represent s.e.m. Baseline response is 100% (dashed line). Potentiated currents from both mutant and wild-type receptors were significantly different from current prior to activation of the light or application of pregnenolone sulfate (paired t test, P < 0.05). Potentiation of mutant receptors was significantly less than potentiation of wild-type receptors (Student's t test, P < 0.05). Recordings were performed with CsMeSO4 internal solution at −60 mV.