The distribution and density of ET-1 and its receptors are different in human right and left ventricular endocardial endothelial cells

Evidence suggests that endocardial endothelial cells (EECs) may play a role in the regulation of cardiac function by releasing ET-1. Furthermore, reports in the literature suggested that differences may exist in peptide receptor distribution between the left and right EECs. In this study, we verified if the distribution and density of ET-1 and its receptors could be different in right as compared to left ventricular EECs, and whether this difference may affect ET-1-induced increase of intracellular calcium. Using immunofluorescence and 3D confocal microscopy, our results showed that in both cell types, the ETA receptor is present and is homogeneously distributed throughout the two cell types. The relative density of the ETA receptor is similar in both right and left ventricular EECs. The ETB receptor is also present in right and left ventricular EECs, however, the relative density of the ETB receptor is higher in the nucleus as compared to the cytosol. In addition, the ETB receptor density was found to be higher in left EECs as compared to right EECs. In addition, our results showed that ET-1 is present in the cytosol and the nucleus of both types of cells and that the relative density of ET-1 is higher in right as compared to left ventricular EECs. Moreover, using the Fura-2 calcium measurement technique, our results showed that in left ventricular EECs, both ETA and ETB receptor activation mediated the effect of ET-1 on intracellular calcium, whereas in right ventricular EECs, this effect was solely mediated by the ETA receptor. In conclusion, our results showed that ET- 1 and its receptors are present in both right and left ventricular EECs. However, the distribution and relative density of ET-1 and its receptors seem to be different in right EECs as compared to left EECs. (c) 2005 Elsevier Inc. All rights reserved.