Angiotensin II and its receptors in human endocardial endothelial cells: role in modulating intracellular calcium

Abstract

he aims of the present study are to investigate the presence and distribution of angiotensin II (Ang II), as well as AT1and AT2receptors, in endocardial endothelial cells (EECs) and to determine if the effect of Ang II on intracellular calcium in these cells is mediated via the AT1or the AT2receptor. Immunofluorescence and 3D confocal microscopy techniques were used on 20-week-old fetal human EECs. Our results showed that Ang II and its receptors, the AT1and the AT2types, are present and exhibit a different distribution in human EECs. Ang II labelling is found throughout the cell with a fluorescence signal higher in the cytosol when compared with the nucleus. Like Ang II, the AT1receptor fluorescence signal is also homogeneously distributed in human EECs but with a preferential labelling at the level of the nucleus, while the AT2receptor labelling is solely present in the nucleus. Using fluo-3 and 3D confocal microscopy technique, superfusion of human EECs with increasing concentration of Ang II induced a dose-dependent sustained increase in free cytosolic and nuclear Ca2+levels. This effect of Ang II on human EEC's intra cellular Ca2+([Ca2+]i) was completely prevented by losartan, an AT1receptor antagonist. Our results suggest that Ang II, as well as AT1and AT2receptors, is present but differentially distributed in EECs of 20-week-old fetal human hearts, and that the AT1receptor mediates the effects of Ang II on [Ca2+]iin these cells.Key words: angiotensin II, nuclear receptors, endocardial endothelial cells, Ang II receptors, intracellular calcium.