Inhibition of smooth muscle cell calcium mobilization and aortic ring contraction by lactone vastatins

Abstract

To determine the effects of vastatins on the contraction of rat aortic rings and to assess their effects on calcium mobilization using cultured smooth muscle cells from rat aorta. Aortic rings from Sprague-Dawley rats were mounted on stainless steel wires to determine the generation of tension using force-displacement transducers. The tension (g) developed by angiotensin II (100 nmol/l) was measured under basal conditions and after 45 min incubation with 20 micromol/l simvastatin. The effect of 20 mol/l simvastatin, lovastatin, mevastatin and pravastatin on noradrenaline concentration-response curves and the angiotensin II-induced calcium mobilization was also evaluated. Addition of angiotensin II to aortic rings incubated in Krebs' Ringer bicarbonate medium produced tension generation (0.9 +/- 0.12 g = 100%). Treatment of aortic rings with simvastatin inhibited the angiotensin II-induced contraction 58 +/- 0.06%. To evaluate this effect further, dose-response curves with noradrenaline were measured in the presence and absence of 20 micromol/l simvastatin, lovastatin, mevastatin and pravastatin. The results indicate that simvastatin, lovastatin and mevastatin inhibited the contraction induced by noradrenaline (10 micromol/l) by about 50%. Pravastatin did not inhibit aortic ring contraction. Furthermore, the concentration required for 50% of the maximal contraction (EC50) by noradrenaline (6.2 +/- 0.1 nmol/l) was significantly increased by simvastatin, lovastatin, mevastatin and pravastatin. The inhibition of vascular contraction by vastatins appears to involve inhibition of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase activity because the inhibitory effect of simvastatin was reduced 50% by 10 mmol/l mevalonic acid. To determine whether the depression of vascular contraction by these agents was correlated with cell calcium changes, the angiotensin II-induced calcium mobilization was determined in Fura-2 loaded cells, before and after treatment with these inhibitors. Simvastatin, lovastatin and mevastatin significantly reduced the angiotensin II-induced calcium mobilization. The concentration that induced 50% inhibition was 3.3 micromol/l for simvastatin, 17.4 micromol/l for mevastatin and 21.7 micromol/l for lovastatin. No effect of pravastatin on calcium mobilization was observed. These findings suggest that lactone vastatins depress vascular contraction by reducing cytosolic calcium release in vascular smooth muscle cells. These agents also appear to exert competitive and non-competitive type antagonisms on noradrenaline action.