Laboratory Investigation

Kidney International (1994) 46, 675–682; doi:10.1038/ki.1994.320

Glucocorticoid uncoupling of antiogensin II-dependent phospholipase C activation in rat vascular smooth muscle cells

Jeffrey R Schelling, Dennis J DeLuca, Martha Konieczkowski, Rochelle Marzec, John R Sedor, George R Dubyak and Stuart L Linas

Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio; Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado; and Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio

Correspondence: Stuart L Linas MD, Denver General Hospital, Department of Medicine, Box 4000, 777 Bannock Street, Denver, Colorado, 80204, USA.

Received 9 February 1994; Revised 13 April 1994; Accepted 14 April 1994.

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Abstract

Glucocorticoid uncoupling of angiotensin II-dependent phospholipase C activation in rat vascular smooth muscle cells. Vascular tone is maintained by both angiotensin II (Ang II) and glucocorticoids, but the effect of glucocorticoids on Ang II function in vascular smooth muscle cells (VSMC) is unclear. To determine the direct influence of glucocorticoids on VSMC Ang II receptor function, the effects of dexamethasone on Ang II receptor binding, Ang Il-induced phospholipase C (PLC) activation, and Ang II-dependent cell growth were studied in cultured rat VSMC. Dexamethasone caused concentration- and time-dependent increases in Ang II binding which were prevented by glucocorticoid receptor inhibition with RU 38486. Dexamethasone-induced enhancement of Ang II binding resulted from increased AT1 receptors, as indicated by Northern blot analysis and competitive binding assays. Despite causing increased Ang II receptor number, dexamethasone preincubation prevented Ang II-induced PLC activation, as indicated by phosphatidylinositol 4,5-bisphosphate degradation and inositol trisphosphate formation. When PLC activity was directly measured in VSMC soluble and membrane fractions, Ang II receptor activation caused decreased soluble and increased membrane PLC activity, consistent with the interpretation that Ang II caused cytosol-to-membrane PLC translocation. The effect of Ang II on PLC translocation was prevented by dexamethasone preincubation. Finally, prolonged incubation with dexamethasone and Ang II had additive effects on VSMC hypertrophy. In conclusion, glucocorticoids directly altered Ang II function in VSMC by causing increased Ang II receptor number, Ang II receptor/PLC uncoupling, and enhanced Ang II-dependent hypertrophy.

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