Angiotensin II increases proto-oncogene expression and phosphoinositide turnover in vascular smooth muscle cells via the angiotensin II AT1 receptor

Abstract

Objectives: The aim of this study was to determine which angiotensin II receptor (AT receptor) mediates proto-oncogene expression and phosphoinositide metabolism in vascular smooth muscle cells in vitro. Design: The AT receptor antagonists DuP753 (losartan), an AT₁ antagonist, and PD 123319, an AT₂ antagonist, were used to characterize AT receptors on cultured vascular smooth muscle cells derived from the rat mesenteric artery and to identify which receptor subtype mediates the angiotensin II-induced increase in proto-oncogene expression and phosphoinositide metabolism. Methods: Rat mesenteric artery vascular smooth muscle cells were grown using standard cell culture methods. Proto-oncogene induction was measured using Northern blotting. Phosphoinositide breakdown was assessed by measuring [³H]-inositol phosphates released from prelabelled cells. Results: Receptor-binding studies revealed that the AT₁ receptor predominated on vascular smooth muscle cells. Incubation of quiescent cells with 0.1 μmol/l angiotensin II resulted in a 65% increase in total [³H]-inositol phosphates released compared with unstimulated cells and in a rapid accumulation of c-fos messenger RNA (mRNA). Pre-incubation of the cells with 10⁻⁵mol/l PD 123319 had no effect on either total inositol phosphates release or c-fos mRNA induction. Both responses, however, were totally abolished by pre-incubation of the cells with 10⁻⁵mol/l losartan or saralasin. Conclusions: Angiotensin II acts through the AT₁ receptor to increase c-fos expression and phosphoinositide turnover in vascular smooth muscle cells. These mechanisms may be important in angiotensin II-induced smooth muscle hypertrophy.