Myocardial beta-adrenoceptors and inhibitory G-proteins in myocardial biopsies and in explanted hearts from patients with dilated cardiomyopathy.

Cardiac beta-adrenoceptors and the alpha-subunits of the inhibitory guanine-nucleotide binding proteins (Gi alpha) were determined in myocardial biopsies and in larger samples of explanted hearts from patients with dilated cardiomyopathy. The myocardium of one non-failing heart was studied for comparison. There were fewer beta-adrenoceptors in right and left ventricular samples from hearts with dilated cardiomyopathy than in the non-failing myocardium. The number of beta-adrenoceptors determined by equilibrium saturation experiments closely correlated with their density as measured by a saturating concentration of the radioligand 125Iodocyanopindolol in myocardial biopsies. Using the 32P-ADP-ribosylation of a 40kDa membrane protein catalyzed by pertussis toxin, an increase of Gi alpha could also be shown in both myocardial biopsies and explanted hearts.