Binding of the hydrophilic β-adrenergic antagonist [3H]CGP-12177 to cardiac tissue slices: characterization and ontogenetic studies in dogs

Abstract

A new technique was developed to characterize the binding of a hydrophilic β-adrenergic antagonist, [³H]CGP-12177, to 1-mm thick slices of canine cardiac tissue. This technique was used to quantify the density (B_max) and the affinity (K_d) of these receptors in the right ventricular conus (RVC) and the left ventricle (LV) at day 1 to 6 weeks of age, and in the adult. Binding was found to be reversible, saturable, stereospecific, of high affinity, and thermolabile. There was an increase in the density of β-adrenergic receptors between day 1 (B_max = 2.2 ± 0.3 fmol/mg tissue in RVC and 2.9 ± 0.8 fmol/mg tissue in the LV) and 2 weeks of age postnatally, after which it remained constant until 6 weeks of age (B_max = 7.5 ± 0.4 and 6.8 ± 0.9 fmol/mg tissue in RVC and LV, respectively); however, by 6 weeks of age it had not reached adult levels (10.3 ± 1.0 fmol/mg tissue). The affinity of these receptors did not change between early neonatal life (K_d = 1.3 ± 0.4 nM) and adulthood (K_d = 1.4 ± 0.2 nM). The density of β-adrenergic receptors in the RVC was similar to that in the LV. This new method of quantifying β-adrenergic receptors in cardiac tissue is simple and fast, and requires minimal tissue handling. It proved to be useful in studying the development of cardiac β-adrenergic receptors with age.