Angiotensin II receptors' modulation of calcium homeostasis in human vascular endothelial cells

Angiotensin II (AngII) plays an important role in the regulation of vascular smooth muscle function. However, little is known about AngII and its receptors AT(1) (AT(1)R) and AT(2) (AT(2)R) and their modulation of intracellular calcium in vascular endothelial cells (VECs) in general and more particularly of human origin. Using western blots, our results showed that AT(1)Rs and AT(2)Rs are present in human VECs (hVECs). Using quantitative 3D confocal imaging, our results showed that AngII is present at the cytoplasmic and nucleoplasmic levels and its relative density is lower in the nucleoplasm. However, both AngII receptors AT(1) and AT(2) are present at both the plasma and the nuclear envelope membranes (NEMs). AngII (10-10 mol/L) induces a transient decrease of the relative density of cytosolic and nuclear AT(1)Rs. Blockade of AT(1)Rs with losartan or blocking protein synthesis with cycloheximide does not prevent internalization and nuclear translocation of AT1Rs but prevents de novo AT(1)R synthesis. In addition, AngII induces cytosolic and nuclear increases (EC50 near 5 x 10(-14) mol/L) of calcium via the activation of AT(1)Rs. These results demonstrate that both AT(1) and AT(2) receptors are present in hVECs, and that only AT(1)Rs seem to undergo transcellular trafficking and modulate cytosolic and nuclear calcium homeostasis.