Angiotensin II-elicited signal transduction via AT(1) receptors in endothelial cells

1 Angiotensin II (AII) actions are mediated by two distinct types of receptors: AT,, which includes two subtypes, AT(1A) and AT(1B), and AT(2). AII produces vasoconstriction on the vascular wall acting directly on smooth muscle cells via AT(1) receptors. AII receptors have recently been demonstrated on endothelial cells. But the pharmacological characteristics of these receptors and the intracellular signal pathways coupled to them remain unclear. 2 The aim of this work was to characterize the AII receptor subtypes in rat aortic endothelial cells (RAEC) in primary culture and to evaluate the signal pathways coupled to these receptors by measuring the activation of phospholipase C (PLC) and phospholipase A(2) (PLA(2)). 3 Labelled AII bound to RAEC in a specific, saturable manner. Scatchard analysis showed a K-d of 1.87 +/- 0.49 nM and a B-max of 50.2 +/- 10.9 x 10(3) sites per cell. AII was displaced by the AT(1)-specific antagonist, DuP753 with a K-i of 17.37 +/- 1.49 nM, but not by the AT(2) receptor analogues CGP42771B or PD123177. These data were confirmed by the finding of AT(1) mRNA in endothelial cells. Analysis of RNA expression by RT-PCR showed the presence of both subtypes, AT(1A) and AT(1B), in endothelial cells, whereas smooth muscle cells express only AT(1A). 4 The activation of PLC and PLA(2) in response to AII was evaluated by measuring inositol phosphate production and arachidonic acid release, respectively. Both were enhanced by AII in a dose-dependent manner, and inhibited by DuP753, but not by PD123177. 5 We conclude that AT(1) receptors are expressed by endothelial cells in primary culture and that phospholipase C and phospholipase A(2) are activated via this receptor.