Effects of verapamil on the binding properties of rat heart muscarinic receptors: evidence for an allosteric site.

The calcium channel antagonist verapamil is known to inhibit competitively antagonist binding to rat heart muscarinic receptors. The present data suggest that this drug recognized two binding sites on the muscarinic receptors: 1) an allosteric site modulating the tracer dissociation rates and 2) the muscarinic drug binding site. The affinity of verapamil for the allosteric site and the efficacy of its effect on muscarinic ligand dissociation rates depended on the ligand studied.