Binding of [125J]-cyanopindolol to ß2-adrenoreceptors and a second unusual binding site in the vessel wall of porcine aorta

Purpose Characterization of radioligand binding for [125J]-cyanopindolol in the vessel wall of the porcine aorta. Methods Radioligand binding for the characterization of [125J]-cyanopindolol binding sites was performed according to Brodde et al., 1981. Results Two [125J]-cyanopindolol binding sites were found in the vascular muscle membranes of the porcine aorta, only the higher-affinity site could be assigned as ß2-adrenoceptor. The assumption that "atypical" ß-adrenoceptors are related to the low affinity site may not be confirmed. The low affinity binding was displaced by (+) isoprenaline, (-) adrenaline and (-) noradrenaline with the same affinity and no stereoselectivity was detected for (-) -isoprenaline. Therefore, the second binding site is no adrenoceptor. Conclusion [125J]-cyanopindolol bound in vascular muscle membranes of the media except to ß2- adrenoceptors (KD 10 pM) to a second low-affinity binding site (KD > 100 nM). For the low-affinity component, a binding of the radioligand to α-adrenoceptors, “atypical" ß-adrenoceptors and serotonin receptors could be excluded. However, further statements on the character of the low-affinity binding site are not yet possible based on the available data.