Effect of Cilazapril and Salt on Ca2+ Extrusion in Arterial Smooth Muscle of Dahl Rats

We examined effects of salt and cilazapril on the Ca pump and Na/Ca exchange system in arterial smooth muscle of Dahl salt-sensitive (DS) rats. Twenty-four DS rats were assigned to four groups. H− and H+ rats were fed a high salt diet; L− and L+ rats were fed a low salt diet. H+ and L+ were administered cilazapril. Aortic rings were superfused with physiologic saline and isometric tension was measured. Relaxation of low Na+-induced contraction was promoted by the removal of external Ca. Cilazapril significantly decreased blood pressure in both the high and low salt diet groups. The inhibition of renin-angiotensin system by cilazapril showed that Ca extrusion by ATP-driven Ca pump was decreased by salt loading, and that Ca extrusion by Na/Ca exchange was increased by salt loading. There was a negative correlation between Ca extrusion by Ca pump and blood pressure, and a positive correlation between Ca extrusion by Na/Ca exchange and blood pressure. These results suggest that the decrease of Ca2+ extrusion by ATP-driven Ca pump resulting from a high salt diet might lead to an elevation in the concentration of cellular Ca2+ and contribute to the mechanism of hypertension in DS rats, and that Ca2+ extrusion by the Na/Ca exchange might be increased in compensation for an increase in cellular Ca2+ concentration on the high salt diet.