Human Aortic Smooth Muscle Cells Containing Angiotensin II Type 1 Receptors

Abstract

We characterized the angiotensin II (All) receptor in human aortic smooth muscle cells (HASMCs). This receptor binds [¹²⁵I]Sar¹, Ile⁸-angiotensin II with a high affinity of 0.20±0.04 nM and a low capacity of 5.3±0.4 fmol/mg protein (230±17 sites/cell). Based on the K₁ values, the ranking order of [¹²⁵I]Sar¹, Ile⁸-AII binding inhibition was as follows: Sar¹, Ile⁸AII > AII > Dup 753 > All > AI » PD 123319. The addition of AII to HASMCs induced a rapid, transient increase in intracellular free Ca²⁺ concentration followed by a lower, sustained phase. When extracellular Ca²⁺ was removed by adding 3 mM EGTA, this initial transient increase was not changed, but the sustained phase was abolished. These results revealed AII receptors in HASMCs to be of the type 1 receptor subtype, which induce Ca²⁺ mobilization mainly from intracellular Ca²⁺ stores.