Endothelium-derived nitric oxide mediates the antiadrenergic effect of human vasostatin-1 in rat ventricular myocardium

Vasostatins (VSs) are vasoactive peptides derived from chromogranin A (CgA), a protein contained in secretory granules of chromaffin and other cells. The negative inotropic effect and the reduction of isoproterenol (Iso)-dependent inotropism induced by VSs in the heart suggest that they have an antiadrenergic function. However, further investigation of the I mechanisms of action of VSs is needed. The aim of the present study was to define the signaling pathways activated by VS-I in mammalian ventricular myocardium and cultured endothelial cells that lead to the modulation of cardiac contractility. Ca2+ and nitric oxide (NO) fluorometric confocal imaging was used to study the effects induced by recombinant human VS-1 [STA-CgA-(1-76)] on contractile force, L-type Ca2+ current, and Ca2+ transients under basal conditions and after P-adrenergic Stimulation in rat papillary Muscles and ventricular cells and the effects on intracellular Ca2+ concentration and NO production in cultured bovine aortic endothelial (BAE-1) cells. VS-1 had no effect on basal contractility of papillary muscle, but the effect of Iso stimulation was reduced by 27%. Removal of endocardial endothelium and inhibition of NO synthesis and phosphatidylinositol 3-kinase (PI3K) activity abolished the antiadrenergic effect of VS-I on papillary muscle. In cardiomyocytes, 10 nM VS-1 was ineffective on basal and Iso (1 mu M)-stimulated L-type Ca2+ current and Ca2+ transients. In BAE-1 cells, VS-I induced a Ca2+-independent increase in NO production that was blocked by the PI3K inhibitor wortmannin. Our results suggest that the antiadrenergic effect of VS-1 is mainly due to a PI3K-dependent NO release by endothelial cells, rather than a direct action on cardiomyocytes.