Decreased binding affinity of olanzapine and clozapine for human muscarinic receptors in intact clonal cells in physiological medium

The binding affinity of olanzapine, clozapine and atropine for muscarinic receptor subtypes in clonal Chinese hamster ovary (CHO) cell lines was compared in intact cells in physiological media to disrupted cells in hypotonic buffer. The affinity of olanzapine and clozapine, but not atropine, for muscarinic receptor subtypes (M-1-M-5) was significantly reduced in intact cells in physiological medium compared to disrupted cells in hypotonic buffer. The affinity of olanzapine for muscarinic M-1 receptors was most affected with a reduction of K-i value from 2.5 to 73 nM in intact cells. These data suggest that the affinity of olanzapine and clozapine for muscarinic receptors have been significantly overestimated. (C) 2000 Elsevier Science B.V. All rights reserved.