Calculation of the dissociation constant Kb of clozapine using the Cheng-Prusoff equation.

The lowest Kb for clozapine were calculated for receptors containing the murine sequence 2 (0.3–1.1 nM). When 5-HT3 receptors contained the human sequence 2, clozapine affinity to the binding site was less potent and Kb ranged from 5.8–13.4 nM. These data demonstrate that the sequence between restriction site BstEII and SgrA1 (defined as sequence 2) of 5-HT3 receptors is important for the binding affinity of clozapine. The calculation of the dissociation constant of clozapine for the P391R mutant revealed a Kb of 1.3 nM. The EC50 for 5-HT (2.73±0.01 µM) has been taken from Thompson et al. (2006) [26].