Roles of nuclear NPY and NPY receptors in the regulation of the endocardial endothelium and heart function.

It is now well accepted that the heart is a multifunctional organ in which endothelial cells, and more particularly endocardial endothelial cells (EECs), seem to play an important role in regulating and maintaining cardiac excitation-contraction coupling. Even if major differences exist between vascular endothelial cells (VECs) and EECs, all endothelial cells including EECs release a variety of auto- and paracrine factors such as nitric oxide, endothelin-1, angiotensin II, and neuropeptide Y. All these factors were reported to affect cardiomyocyte contractile performance and rhythmicity. In this review, findings on the morphology of EECs, differences between EECs and other types of endothelial cells, interactions between EECs and the adjacent cardiomyocytes, and effects of NPY on the heart will be presented. We will also show evidence on the presence and localization of NPY and the Y1 receptor in the endocardial endothelium and discuss their role in the regulation of cytosolic and nuclear free calcium.