[Magnesium ions and contractile activity of vascular smooth muscle cells in hypoxia]

In isolated smooth muscle of the rat portal vein removal of Mg2+ from perfusate induced rapid enhancement of frequency and amplitude of spontaneous contractions and decreased inhibiting effect of hypoxia on the smooth muscle contractile activity. Concomitant elevation of extracellular Ca2+ has no additional protective effect on the smooth muscle in hypoxia. Ten-fold lowering of Mg2+ content in buffer solution resulted in a significant rise in the tension of the smooth muscle activated by Ca2+. The data obtained suggest that protective effect of Mg2+-free solution on vascular smooth muscle in hypoxia may be mediated not only through increases intracellular Ca2+ concentration but also due to rising sensitivity of the smooth muscle cells contractile protein to Ca2+.