Effects Of Mg²⁺ On The Contractile Response And Endothelium-dependent Relaxation In Pulmonary Artery Of Mice

Magnesium is an essential element which has imporatant functions in the body. Studies have indicated that Mg²⁺ plays an important role in regulating function of vascular smooth muscle cells function and endothelial cells. Mg²⁺ regulates vascular tone through the effects on Ca²⁺ channel of vascular smooth muscle cells and agonist-contraction coupling. Besides, Mg²⁺ affects the vascular reactivity to the vasoconstrictor and vasodilator. Many epidemiological, clinical and experimental studies have confirmed that Mg²⁺ plays an important role in the regulation of vascular tone in hypertension, but the role of Mg²⁺ in the regulation pulmonary vascular tone has rarely been studied. In this study, we observed the effects of Mg²⁺ on PAs contraction induced by different agnoists using KCl, CPA, OAG and ET-1. The effects of Mg²⁺ on endothelium-dependent vasodilation was observed by using acetylcholine（ACh） and L-NAME, an inhibitor of nitric oxide synthase. Providing as experiment and theory foundations to study the mechanism of Mg²⁺ regulating pulmonary vascular function and changes in PH.Objective: To investigate the the effects of Mg²⁺ on PAs contraction induced by different agnoists and the effects of Mg²⁺ on endothelium-dependent vasodilation, providing as experiment and theory foundations to study the mechanism of Mg²⁺ regulating pulmonary vascular function and changes in PAH.Methods: Using micro vessel tension detection technique, in the absence of Mg²⁺（0.0m M）, normal Mg²⁺（1.2mm） and high Mg2 + 4.8m M situation,（1） using three different types of calcium channel agnoists KCl, CPA and OAG to investigate the effects of Mg²⁺ on contraction of PAs without endothelium from normal mice mediated by three different types of calcium entry;（2） investigate the effects of Mg²⁺ on contraction of PAs without endothelium induced by ET-1;（3）investigate the effects of Mg²⁺ on contraction of PAs with endothelium induced by ET-1, compare the differences in the presence and absence of endothelium;（4） observe the effects of Mg²⁺ on endothelium-dependent vasodilation, and the difference in the presence of L-NAME.Results: 1.The effects of Mg²⁺ on the contractile response of PAs without endothium mediated by different types of caclium entry.（1）In the absence of Mg²⁺, the contraction of PAs caused by KCl was significantly lower than that of normal Mg²⁺, but there is not difference between high Mg²⁺ and normal Mg²⁺. This result suggested that the vasoconstriction induced by Ca²⁺ entry through voltage dependent calcium channels（VDCC） required the presence of Mg²⁺, but high Mg²⁺ does not affects Ca²⁺ entry through VDCC.（2） In the absence of Ca²⁺, the contraction of PAs caused by CPA was significantly higher in the absence of Mg²⁺ than that of normal Mg²⁺ and lower in high Mg²⁺. In the presence of 2m M Ca Cl2, the contraction of PAs was significantly lower in high Mg²⁺, but there is no difference between absence of Mg²⁺ and normal Mg²⁺. This result suggested that Ca²⁺ release from sarcoplasmic reticulm is enhanced in the absence of Mg²⁺, while high Mg²⁺ inhibited the release and entry of Ca²⁺ induced by CPA. High Mg²⁺ can inhibit the the vascular contraction mediated by SOCE.（3）OAG did not induce significant contraction, and there was no significant difference in different concentrations of Mg²⁺, suggest that Mg²⁺ has no significant effect on the function of ROCE in normal PAs. 2.The effect of Mg²⁺ on the contractile response of PAs without endothium mediated by ET-1. The contraction of PAs without endothelium caused by ET-1 was significantly lower in the absence of Mg²⁺ and high Mg²⁺ than that of normal Mg²⁺, the EC50 was higher and Emax was lower. This effect suggest that vasoconstriction induced by ET-1 required the presence of Mg²⁺, and high Mg²⁺ can inhibit the contraction. 3. The effect of Mg²⁺ on the endothelium-dependent vasodilation of PAs.（1） The contraction of PAs with endothium caused by ET-1 was significantly lower in the absence of Mg²⁺ and high Mg²⁺ than that of normal Mg²⁺, the EC50 was higher and Emax was lower. In the absence of Mg²⁺, the EC50 and Emax of ET-1 was no difference with and without endothelium, but the EC50 was higher and Emax was lower with endothelium. This effect suggest that Mg²⁺ is necessary for endothelium-dependent vasodilation of PAs, high Mg²⁺ could significantly enhance the endothelium-dependent vasodilation.（2）In the absence of Mg²⁺, the concentration-dependent vasodilation by ACh was significantly lower than that of normal Mg²⁺, but higher in high Mg²⁺. The concentration-dependent vasodilation by ACh was significantly inhibited in different concentrations of Mg²⁺ in the presence of NOS inhibitor L-NAME. This effect suggest that the synthesis of vasodilator（NO） by endothelial cells required the presence of Mg²⁺, high concentration of Mg²⁺ can promote the synthesis of NO.Conclusion: 1.Mg²⁺ can inhibit the PAs contraction induced by Ca²⁺ release from sarcoplasmic reticulm in a dose-dependent manner. There is not significant effect on the PAs contraction induced by SOCE in the absence of Mg²⁺, while high Mg²⁺ can inhibit the function of SOCE. 2. The PAs contraction induced by ET-1 was inhibited in the absence of Mg²⁺ as well as high Mg²⁺. The PAs contraction induced by Ca²⁺ entry mediated by VDCC was inhibited in the absence of Mg²⁺, but not in high Mg²⁺. 3. Mg²⁺ can enhenced the endothelium-dependent vasodilation of PAs in a dose-dependent manner. Mg²⁺ can stimulate NO synthes of endothelial cells to promote endothelium-dependent vasodilation of PAs.