Contractile effects by intracellular angiotensin II via receptors with a distinct pharmacological profile in rat aorta

1 We studied the effect of intracellular angiotensin II (Ang II) and relate d peptides on rat aortic contraction, whether this effect is pharmacologica lly distinguishable from that induced by extracellular stimulation, and det ermined the Ca2+ source involved. 2 Compounds were delivered into the cytoplasm of de-endothelized aorta ring s using multilamellar liposomes. Contractions were normalized to the maximu m obtained with phenylephrine (10(-5) M). 3 Intracellular administration of Ang II (incorporation range: 0.01 - 300 n mol mg(-1)) resulted in a dose-dependent contraction, insensitive to extrac ellular administration (10(-6) M) of the AT(1) receptor antagonist CV11947, the AT(2) receptor antagonist PD 123319, or the non-selective AT receptor antagonist and partial agonist saralasin ([Sar(1),Val(5),Ala(8)]-Ang II (P < 0.05). 4 Intracellular administration of CV11947 or PD 123319 right shifted the do se-response curve about 1000 fold or 20 fold, respectively. PD 123319 was o nly effective if less than 30 nmol mg(-1) Ang II was incorporated. 5 Contraction was partially desensitized to a second intracellular Ang II a ddition after 45 min (P < 0.05). 6 Intracellular administration of Ang I and saralasin also induced contract ion (P < 0.05). Both responses were sensitive to intracellular CV11947 (P < 0.05), but insensitive to PD 123319. The response to Ang I was independent of intracellular captopril. 7 Contraction induced by extracellular application of Ang II and of Ang I w as abolished by extracellular pre-treatment with saralasin or CV11947 (P < 0.05), but not with PD 123319. Extracellular saralasin induced no contracti on. 8 Intracellular Ang II induced contraction was not affected by pre-treatmen t with heparin filled liposomes, but completely abolished in Ca2+-free exte rnal medium. 9 These results support the existence of an intracellular binding site for Ang II in rat aorta. Intracellular stimulation induces contraction dependen t on Ca2+-influx but not on Ins(1,4,5)P-3 mediated release from intracellul ar Ca2+-stores. Intracellular Ang I and saralasin induce contraction, possi bly via the same binding site. Pharmacological properties of this putative intracellular receptor are clearly different from extracellular stimulated AT(1) receptors or intracellular angiotensin receptors postulated in other tissue.