Fig. 4. Ketamine inhibition of the homologous mutation in 5HT^3A. (A ) A control current activated by 2 μm serotonin from 5HT^3AS258A before (left ) and during a second serotonin application with 20 μm ketamine (middle ), and after ketamine washout (right ). (B ) Bar graph demonstrates current remaining in the presence of 20 μm ketamine in 5HT^3AS258A compared to the wild-type serotonin receptor and the wild-type α7 nicotinic receptor. (C ) Concentration response relationship for ketamine inhibition of the activation of 5HT^3AS258A receptor (▪) and the wild-type 5HT^3Areceptor (○). The IC⁵⁰for ketamine inhibition of 5HT^3AS258A was 158 ± 42 μm ketamine (Hill coefficient, 0.6 ± 0.1). Ketamine inhibition of the S258A mutant was significantly greater than for the wild-type receptor (ANOVA, P < 0.001). Number of oocytes for each data point = 5–11. Values are expressed as mean ± SE.