Magnesium regulation of Ca2+ channels in smooth muscle and endothelial cells of human allantochorial placental vessels

In human allantochorial placental vessels, the vascular tone is regulated b y membrane potential controlled by the ion flux through K+ and Ca2+ channel s. The effects of MgCl2 and MgSO4 were studied on the membrane potential of vascular smooth muscle cells [VSMCs) and of endothelial cells (VECs). The membrane potential was the main factor of the excitation-contraction coupli ng of placental vessels. The VSMCs and VECs were predepolarized by high ext ernal K+, which blocked voltage-sensitive K+ channels, and depolarized by s erotonin addition which activated Ca2+ influx through voltage-gated Ca2+ ch annels. Addition of MgCl2 or MgSO4 in the external medium induced a depolar ization level lower than the previous level, as nifedipine a Ca2+ blocker, corresponding to a Ca2+ influx reduction in VSMCs and VECs and inducing rel axation of the cells. The effect of MgCl2 and MgSO4 was the same on VSMCs a nd VECs, but the depolarization level reduction was more important with MgC l2 than MgSO4 on VSMCs. These data suggest ed that Mg salts regulated the C a2+ influx through voltage-gated Ca2+ channels in VSMCs and VECs and conseq uently the tonus of human allantochorial placental vessels and that there w as a difference between Mg salts.