Figure 2. The muscarinic inhibitory activity of S(+) and R(-) ketamine. Oocytes expressing the m1 muscarinic receptor were voltage clamped at -70 mV, and inward Cl sup - current was recorded in response to 10 sup -7 M acetyl-beta-methylcholine. At least five oocytes were used to determine each data point. (A) The concentration-inhibition relation of S(+) ketamine. The calculated median inhibitory concentration (IC⁵⁰) is 125 +/- 33 micro Meter, and the Hill coefficient is 1.1. (B) The concentration-inhibition relation of R(-) ketamine. The calculated IC⁵⁰is 91 +/- 19 micro Meter, and the Hill coefficient is 1.1. (C) The concentration-inhibition relation of equimolar S(+)/R(-) ketamine. The calculated 1C⁵⁰is 48 +/- 1 micro Meter, and the Hill coefficient is 1.5. (D) An isobologram of the interaction between S(+) and R(-) ketamine. The interaction is synergistic, and R is 2.2. *P = 0.025.