(±)[125Iodo]cyanopindolol, a new ligand for β-adrenoceptors: Identification and quantitation of subclasses of β-adrenoceptors in guinea pig

Abstract

(±)[125Iodo]cyanopindolol (ICYP) is a radioligand which binds with an extraordinarily high affinity and specificity to β-adrenoceptors. In contrast to (±)[125Iodo]-hydroxybenzylpindolol (IHYP), the new ligand has neither affinity to α- nor to 5-HT-receptors. The dissociation constants of ICYP for β-adrenoceptors in various tissues range from 27 to 40 pM, thereby exceeding the affinity of IHYP by a factor of ∼ 3. ICYP does not discriminate between β1- and β2-. Therefore, the densities of the two receptor subtypes can be determined from competition curves of ICYP by drugs previously found to show in vitro selectivity for β1-adrenoceptors. The guinea pig left ventricle contains only β1- adrenoc..