Binding properties of beta-adrenergic receptors in oviductal smooth muscle membranes

In particular membrane fractions of human and rabbit oviductal smooth muscle specific binding sites for the radiolabelled beta-adrenergic antagonist [125I]- cyanopindolol (I- CYP ) were detectable utilizing the radioligand technique. The binding was saturable, relative to the concentration of protein as well as ligand in the assay. The analysis of the binding kinetics by Scatchard plots revealed a number of beta-adrenergic receptor sites of 30 fmol I- CYP bound per milligram protein with a dissociation constant (KD) of 20 pM. In competition binding studies with beta 2-adrenergic agonists and antagonists the receptors in their pharmacological range corresponded to the beta 2-subtype of beta-adrenergic receptors. Within the oviduct the ampulla possessed 70% of all traceable beta-adrenergic receptor sites.