Binding of ¹²⁵I-Cyanopindolol to Beta-1-Adreno-Ceptors in a High and Low Affinity State

Abstract

Investigation of binding properties of (+), (−) and (±)¹²⁵Iodocyanopindolol (ICYP) to ß₁-adrenoceptors of guinea pig left ventricle membranes revealed that these radioligands bind to receptors in a high and low affinity state which is not influenced by guanylnucleotides. The contribution of the (+)enantiomer to the binding of the racemic ligand at low receptor concentrations can be neglected since the dissociation time courses of (±) and (−)ICYP are identical. The existence of two affinity states of ß-adrenoceptors interacting with the antagonist ICYP was evident from 1: biphasic dissociation kinetics and 2: from curvilinear Scatchard plots.