Effects of the β3 -Adrenergic Agonist BRL 37344 on Endothelial Nitric Oxide Synthase Phosphorylation and Force of Contraction in Human Failing Myocardium

• Published in: Journal of cardiac failure 2009-02, Vol.15 (1), p.57-67
• Main Authors: Napp, Andreas, MD, Brixius, Klara, PhD, Pott, Christian, MD, Ziskoven, Christoph, MD, Boelck, Birgit, PhD, Mehlhorn, Uwe, MD, Schwinger, Robert H.G., MD, Bloch, Wilhelm, MD
• Format: Article
• Language: English
• Subjects: Cardiovascular
• ISSN: 1071-9164
• DOI: 10.1016/j.cardfail.2008.08.006

Abstract Background In nonfailing myocardium, β3 -adrenergic signaling causes a decrease in contractility via endothelial nitric oxide synthase (eNOS) activation and nitric oxide (NO) release. This study investigates the hypothesis that β3 -adrenergic signaling undergoes alterations in failing myocardium. Methods We compared eNOS- and β3 -adrenoceptor expression using Western blot analysis in human nonfailing myocardium versus failing myocardium. With the use of immunohistochemistry, we investigated the distribution of the β3 -adrenoceptor protein and eNOS translocation and phosphorylation under basal conditions. β3 -adrenergic, eNOS activation, and inotropy were measured in failing myocardium using BRL37344 (BRL, a β3 -adrenoceptor agonist). Results β3 -adrenoceptor expression was increased in failing myocardium. Under basal conditions, Akt- and eNOSSer1177 phosphorylation were reduced in failing myocardium. During stimulation with BRL in failing myocardium, a further dephosphorylation of eNOSSer1177 and Akt was observed, whereas eNOSSer114 phosphorylation was increased. These results suggest a deactivation of eNOS via β3 -adrenergic stimulation. Nevertheless, BRL decreased contractility in failing myocardium, but this effect was not observed in the presence of the NO blocker L-NMA. In failing myocardium, the β3 -adrenoceptor was predominantly expressed in endothelial cells. In the cardiomyocytes, the β3 -adrenoceptor was mainly located at the intercalated disks. Conclusion In failing cardiomyocytes, β3 -adrenergic stimulation seems to deactivate rather than activate eNOS. At the same time, β3 -adrenergic stimulation induced a NO-dependent negative inotropic effect. Because β3 -adrenoceptors are expressed mainly in the endothelium in failing myocardium, our observations suggest a paracrine-negative inotropic effect via NO liberation from the cardiac endothelial cells.