Mechanisms of β3‐adrenoceptor‐induced eNOS activation in right atrial and left ventricular human myocardium

β‐adrenoceptors are important modulators of cardiac function. The present study investigated β3‐adrenergic eNOS activation in human myocardium. We measured nitric oxide (NO) liberation (diaminofluorescence) and signal transduction (immunohistochemistry, phosphorylation of eNOSSer1177, eNOSThr495, eNOSSer114, Akt/protein kinase B (Akt/PKB), and eNOS translocation) in human right atrial (RA, aortocoronary‐bypass OP) and left ventricular nonfailing (LV, rejected donor hearts) myocardium after application of BRL 37344 (BRL), a preferential β3‐adrenoceptor agonist. In both RA and LV, BRL (10 μl) induced a liberation of NO. An eNOS activation via translocation was only observed in RA after application of BRL (10 μM). Yet, the NO liberation in both LV and RA was accompanied by phosphorylation of eNOSSer1177 and Akt/PKB. BRL‐induced eNOS phosphorylation was abolished by LY292004, a blocker of PI‐3 kinase. eNOS‐Ser114 phosphorylation was unchanged in RA, but decreased in LV after β3‐adrenergic stimulation. BRL did not alter phosphorylation of eNOSThr495. In conclusion, receptor‐dependent eNOS activation is differentially regulated in the human heart. In the left ventricle, eNOS activation via phosphorylation seems to be of major importance, whereas in human atrial myocardium eNOS translocation is the predominant mechanism induced by β3‐adrenergic activation. British Journal of Pharmacology (2004) 143, 1014–1022. doi:10.1038/sj.bjp.0705983