p-Fluoro-hexahydro-sila-difenidol: affinity for vascular muscarinic receptors

The M3-selective antagonist, p-fluorohexahydro-sila-difenidol was used to characterize muscarinic receptors in two vascular preparations, the rabbit ear artery with an endothelium-dependent relaxation and the bovine coronary artery with an endothelium-independent contractile response. pKB values were consistent with the presence of M3 receptors, 7.9 and 7.5 in coronary and ear arteries, respectively. These findings confirm that muscarinic receptors of the rabbit ear artery and bovine coronary artery have similar characteristics and belong to the M3 subtype.