β3-Adrenergic eNOS stimulation in left ventricular murine myocardium

Abstract

This study investigates mechanisms underlying β₃-adrenergic activation of the endothelial nitric oxide synthase (eNOS) in myocardial tissue of wild-type (WT) and β₃-adrenoceptor knockout (β₃-KNO) mice, in the absence and presence of BRL 37344 (BRL), the preferential β₃-adrenoceptor selective agonist. Nitric oxide (NO)-liberation was measured after the application of BRL (10 µmol/L), using fluorescence dye diaminofluorescein (DAF), in left ventricular cardiac preparations. Phosphorylation of eNOS^Ser1177, eNOS^Thr495, eNOS^Ser114, and eNOS translocation, and alterations of 8-isoprostaglandin F2α (a parameter for reactive oxygen radical generation), after application of BRL (10 µmol/L), were studied using immunohistochemical stainings in isolated, electrically stimulated (1 Hz) right atrial (RA) and left ventricular (LV) myocardium. An increased NO release after BRL application (10 µmol/L) was observed in the RA and LV myocardial tissue of WT mice, but not in β₃-KNO mice. This NO liberation in WT mice was paralleled by an increased eNOS^Ser1177, but not eNOS^Thr495, phosphorylation. A cytosolic eNOS translocation was observed after the application of BRL (10 µmol/L) only in the RA myocardial tissue of WT mice. A BRL (10 µmol/L)-dependent increase in eNOS^Ser114 phosphorylation was observed only in the LV myocardial tissue of WT mice; this was paralleled by an increase in 8-isoprostaglandin F2α. In murine myocardium, 3 β₃-adrenoceptor-dependent activation pathways for eNOS exist (i.e., a translocation and phosphorylation of eNOS^Ser1177 and eNOS^Ser114). These pathways are used in a regional-dependent manner. β₃-adrenergic oxygen-derived free radical production might be important in situations of enhanced β₃-adrenoceptor activation, as has been described in human heart failure.