Cellular adhesion to elements of the extracellular matrix in the hypertensive rat modulates the effect of angiotensin II

This study was to assess the role of different components of the extracellular matrix (ECM) on the mobilization of Ca i ++ induced by angiotensin II in vascular smooth muscle cells (VSMC) from hypertensive (SHR) and normotensive (WKY) rats. The effect of All (10-6 M) on Ca i ++ release was studied in VSMC isolated from the aorta of 5-week-old WKY and SHR using fluorescent imaging microscopy (fura-2). Ca i ++ mobilization was characterized by amplitude, slope of Ca i ++ increase and total amount of Ca i ++ . Cells were cultured on glass coverslips (control) or coated with either collagen I, collagen IV, vitronectin, fibronectin and extracellular matrix (ECM) and studied at confluence between passage 3 and 9. A significant increase of Ca i ++ released by All has been observed with cells from WKY cultured on collagen I (meam±SEM, amplitude: 192±12% of control values, slope: 194±13%, total amount Ca i ++ : 173±12%, n=270, p≤0.0001 for each, unpaired t-test). Conversely, response with SHR was not significatively modified. Ca i ++ mobilization was not significatively modified after culture of VSMC from SHR and WKY on collagen IV. A significative decrease of the slope (WKY: 66±6%, p≤0.0001; SHR: 83±5%, p≤0.03) and of the amount of Ca i ++ (WKY: 74±7%, p≤0.01; SHR: 74±5%, p≤0.01) has been observed after culture of VSMC from the 2 strains on vitronectin. A decrease in amplitude (53±3%, p≤0.0001), slope (38±4% p≤0.0001) and Ca i ++ release (69±5%, p≤0.004, n=106) has been observed in VSMC from SHR seeded on fibronectin. Conversely, in VSMC from WKY, Ca i ++ mobilisation has not been modified compared with control cells. Culture of VSMC from SHR on ECM induced a significative decrease of amplitude (49±2%), slope (54±4%) and Ca i ++ release (53±3%, p≤0.0001 for each, n=122), while in WKY, ECM induced a significative stimulation of these parameters (amplitude: 157±11%, slope: 149±13% and Ca i ++ release: 130±9%, p≤0.0001 for each, n=247). These results show that the Ca i ++ mobilization induced by All is modified by the adhesion of cells to different ECM components. This suggests a modulation of the A II-associated signalling events via the focal adhesion points. Furthermore, a difference in this modulation is observed between SHR and WKY when cells are seeded on collagen I, fibronectin or ECM. These modulations of Ca i ++ mobilization could play a role in the regulation of growth and differentiation of cells during the developement of hypertension.