-adrenoceptor density and relative number of -adrenoceptor subtypes in biopsies from human right atrial, left ventricular, and right ventricular myocard

Abstract

In the present study we estimated the relative number of β-adrenoceptors in membrane preparations from right atrial and left ventricular biopsies from 8 patients, as well as from right ventricular biopsy from one patient. Determinations of relative number of β adrenoceptor subtypes (β₁, β₂) were also performed. Estimations were performed in a radioligand assay, measuring specific binding of [¹²⁵I]-cyanopindolol (CUP). Inhibition of specific [¹²⁵I] CYP binding was studied by adding propranolol (non-selective antagonist), atenolol (β₁ selective antagonist) and ICI 118551 (β₂ selective antagonist) to the preparations. Some individual variance in total number of receptors was found. Per mg protein, the number of binding sites were higher in atrial preparations (mean 71.4 ± 14.4 fmol·mg⁻¹) than in left ventricular preparations (mean 30.2 ± 7.1 fmol·mg⁻¹). Receptor number in the right ventricular preparation was 49.5 ± 2.6 fmol·mg⁻¹. Approximately 25% of β adrenoceptors were of β₂ subtype in preparations from both right atrial and left ventricular biopsies, as well as from the right ventricular biopsy. Thus, there are regional differences in the quantity of β adrenoceptors in human myocard whereas the relative proportion of β₁ and β₂ receptors appears to be fairly constant.