High magnesium mitigates the vasoconstriction mediated by different types of calcium influx from monocrotaline‐induced pulmonary hypertensive rats

New Findings What is the central question of this study? What is the involvement of Mg2+ in mitigating the vasoconstriction in pulmonary arteries and smaller pulmonary arteries in the monocrotaline‐induced pulmonary arterial hypertension (MCT‐PAH) rat model? What are the main finding and its importance? Both store‐operated Ca2+ entry‐ and receptor‐operated Ca2+ entry‐mediated vasoconstriction were enhanced in the MCT‐PAH model. High magnesium inhibited vasoconstriction by directly antagonizing Ca2+ and increasing NO release, and this was more notable in smaller pulmonary arteries. Increased extracellular magnesium concentration has been shown to attenuate the endothelin‐1‐induced contractile response via the release of nitric oxide (NO) from the endothelium in proximal pulmonary arteries (PAs) of chronic hypoxic mice. Here, we further examined the involvement of Mg2+ in the inhibition of vasoconstriction in PAs and distal smaller pulmonary arteries (sPAs) in a monocrotaline‐induced pulmonary arterial hypertension (MCT‐PAH) rat model. The data showed that in control rats vasoconstriction in sPAs is more intense than that in PAs. In MCT‐PAH rats, store‐operated Ca2+ entry (SOCE)‐ and receptor‐operated Ca2+ entry (ROCE)‐mediated contraction were significantly strengthened. However, there was no upregulation of the vasoconstriction mediated by voltage‐dependent calcium entry (VDCE). Furthermore, high magnesium greatly inhibited VDCE‐mediated contraction in PAs rather than sPAs, which was the opposite of the ROCE‐mediated contraction. Moreover, monocrotaline pretreatment partly eliminated the endothelium‐dependent vasodilatation in PAs, which in sPAs, however, was still promoted by magnesium due to the increased NO release in pulmonary microvascular endothelial cells (PMVECs). In conclusion, the findings suggest that both SOCE‐ and ROCE‐mediated vasoconstriction in the MCT‐PAH model are enhanced, especially in sPAs. The inhibitory effect of high magnesium on vasoconstriction can be achieved partly by its direct role as a Ca2+ antagonist and partly by increasing NO release in PMVECs.