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 AT1 (AT1 R) and AT2 (AT2 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 AT1 Rs and AT2 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 AT1 and AT2 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 AT1 Rs. Blockade of AT1 Rs with losartan or blocking protein synthesis with cycloheximide does not prevent internalization and nuclear translocation of AT1 Rs but prevents de novo AT1 R synthesis. In addition, AngII induces cytosolic and nuclear increases (EC50 near 5 × 10-14 mol/L) of calcium via the activation of AT1 Rs. These results demonstrate that both AT1 and AT2 receptors are present in hVECs, and that only AT1 Rs seem to undergo transcellular trafficking and modulate cytosolic and nuclear calcium homeostasis.