ET_A receptors are present in human aortic vascular endothelial cells and modulate intracellular calcium

Using immunofluorescence and real 3-D confocal microscopy, our results showed the presence of ET-1, ET_A, and ET_B receptors in isolated human aortic vascular endothelial cells (hVECs). The level of the peptide and its receptors was significantly higher in the nucleus (including the nuclear envelope membranes) than in the cytosol (including the cell membrane). Furthermore, using the Western blot technique we demonstrated the presence of both ETA and ET_B receptors. Using intact and isolated human hVECs and the Fura-2 calcium (Ca²⁺) measurement technique, we showed that ET-1 induced a dose-dependent increase of total intracellular free Ca²⁺, with an EC50 of 1.3 10^-10 mol/L. The specific ETA receptor antagonist ABT-627 (10^-7 mol/L), but not the ETB receptor antagonist A-192621 (10^-7 mol/L), prevented the ET-1 (10^-9 mol/L) induced increase of total intracellular Ca²⁺. In conclusion, these results clearly show that similar to ETB receptors, ETA receptors are also present in human aortic vascular endothelial cells and their levels are higher than ETB in the nucleus when compared with the cytosol. Furthermore, we suggest that ETA, but not ETB, receptors mediate the effect of ET-1 on total intracellular Ca²⁺ of human aortic vascular endothelial cells.