Beta-adrenoceptor density and relative number of beta-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 beta-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 beta adrenoceptor subtypes (beta1, beta2) were also performed. Estimations were performed in a radioligand assay, measuring specific binding of [125I]-cyanopindolol (CYP). Inhibition of specific [125I] CYP binding was studied by adding propranolol (non-selective antagonist), atenolol (beta1 selective antagonist) and ICI 118551 (beta2 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 X mg-1) than in left ventricular preparations (mean 30.2 +/- 7.1 fmol X mg-1). Receptor number in the right ventricular preparation was 49.5 +/- 2.6 fmol X mg-1. Approximately 25% of beta adrenoceptors were of beta2 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 beta adrenoceptors in human myocard whereas the relative proportion of beta1 and beta2 receptors appears to be fairly constant.