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

The lowest K_b 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 K_b 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 K_b of 1.3 nM. The EC₅₀ for 5-HT (2.73±0.01 µM) has been taken from Thompson et al. (2006) [26].