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

Abstract

1 b-adrenoceptors are important modulators of cardiac function. The present study investigated b 3 -adrenergic eNOS activation in human myocardium. 2 We measured nitric oxide (NO) liberation (diaminofluorescence) and signal transduction (immunohistochemistry, phosphorylation of eNOS Ser1177 , eNOS Thr495 , eNOS Ser114 , 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 b 3 -adrenoceptor agonist. 3 In both RA and LV, BRL (10 ml) induced a liberation of NO. An eNOS activation via translocation was only observed in RA after application of BRL (10 mM). Yet, the NO liberation in both LV and RA was accompanied by phosphorylation of eNOS Ser1177 and Akt/PKB. BRL-induced eNOS phosphorylation was abolished by LY292004, a blocker of PI-3 kinase. eNOS-Ser 114 phosphorylation was unchanged in RA, but decreased in LV after b 3 -adrenergic stimulation. BRL did not alter phosphorylation of eNOS Thr495 . 4 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 b 3 -adrenergic activation.

Induction of β3-Adrenergic Receptor Functional Expression following Chronic Stimulation with Noradrenaline in Neonatal Rat Cardiomyocytes

“…A coupling of ␤ 3 -ARs to G i/o protein and the activation of endothelial nitric-oxide synthase mediate this negative inotropic effect (Gauthier et al, 1998;Kitamura et al, 2000;Varghese et al, 2000;Brixius et al, 2004). Therefore, the modulation of cardiac contractility by the ␤ 3 -ARs seems to involve the inhibition of the adenylyl cyclase and the decreased in intracellular cAMP content.…”

“…In contrast to ␤ 1 -and ␤ 2 -AR, activation of the ␤ 3 -AR induces a negative inotropic effect in different species, including human, dog, guinea pig, and rat (Gauthier et al, 1998(Gauthier et al, , 1999Kitamura et al, 2000;Cheng et al, 2001;Moniotte et al, 2001;Morimoto et al, 2004). ␤ 3 -AR-mediated decrease in cardiac contractility involves coupling to G i/o protein(s) and activation of constitutively expressed endothelial nitric-oxide synthase and the subsequent generation of NO (Gauthier et al, 1998;Kitamura et al, 2000;Varghese et al, 2000;Brixius et al, 2004). Furthermore, the functional activity of ionic currents such as L-type Ca 2ϩ and potassium I(Ks) are reduced by ␤ 3 -AR stimulation, which also modulates cardiac contractility (Kitamura et al, 2000;Cheng et al, 2001;Bosch et al, 2002;Morimoto et al, 2004).…”

Epinephrine Regulation of the Endothelial Nitric-oxide Synthase

“…8 and 9) have explored the roles of adrenergic agonists and antagonists in regulation of the endothelial isoform of nitric-oxide synthase (eNOS), 2 an enzyme that is a key determinant of blood pressure and cardiac myocyte function. In different tissues and experimental systems, diverse adrenergic receptor subtypes, including ␣ 1 (10,11),␣ 2 (12,13), ␤ 1 (14), ␤ 2 (15,16), and ␤ 3 (17,18) adrenergic receptors, have been implicated in the modulation of eNOS, but the pathways involved in the molecular regulation of eNOS by adrenergic pathways remain incompletely understood.…”

Regulation of Endothelial Nitric-oxide Synthase (NOS) S-Glutathionylation by Neuronal NOS

“…By contrast, it is generally accepted that the negative inotropic effect elicited by ␤ 3 -AR stimulation depends on the myocardial release of NO by the endothelial NOS isoform (eNOS) (2)(3)(4). ␤ 3 -ARs are thought to co-localize with eNOS in the sarcolemmal caveolar microdomains of left ventricular (LV) myocytes, and ␤ 3 -AR stimulation has been shown to stimulate eNOS activity (3) and decrease contraction and the [Ca 2ϩ ] i transient amplitude (5,6).…”

“…By contrast, it is generally accepted that the negative inotropic effect elicited by ␤ 3 -AR stimulation depends on the myocardial release of NO by the endothelial NOS isoform (eNOS) (2)(3)(4). ␤ 3 -ARs are thought to co-localize with eNOS in the sarcolemmal caveolar microdomains of left ventricular (LV) myocytes, and ␤ 3 -AR stimulation has been shown to stimulate eNOS activity (3) and decrease contraction and the [Ca 2ϩ ] i transient amplitude (5,6). A neuronal NOS (nNOS) isoform is also constitutively present in the myocardium where it plays an important role in the regulation of inotropy and Ca 2ϩ fluxes, by affecting the S-nitrosylation and phosphorylation state of a number of proteins involved in excitation-contraction coupling (7)(8)(9)(10)(11).…”