마그네슘 이온이 적출한 흰쥐 자궁근의 수축성에 미치는 효과

Effect of Magnesium Ion on the Contractility of the Isolated Rat Uterine Smooth Muscle

The effects of Mg⁺⁺ upon the spontaneous contraction activated by 1 IU/l oxytocin were studied in the isolated rat uterine muscle. Longitudinal muscle strips u¡¤ere prepared from the rat uteri at the estrous stage. All experiments were performed in tris-buffered Tyrode solution which was aerated with 100% O² and kept at 35℃. The results obtained were as follows: 1) In the uterine strips contracting spontaneously, as Mg⁺⁺ concentration increased in the Tyrode solution the amplitude of peak tension decreased in all the experimental solutions containing the various concentrations of Ca⁺⁺(0.5 ~ 4 mM). And the amplitude of peak tension increased in inverse proportion to the [Mg⁺⁺]/[Ca⁺⁺] ratio. It is suggested that the tension-lowering effect of Mg⁺⁺ would be developed through decreasing intracellular ionized free calcium ion concentration by uncertain mechanism. 2) The frequency of the uterine contraction activated by oxytocin increased as the [Mg⁺⁺]/[Ca⁺⁺] ratio ratio increased up to 1/2, but the frequency decreased above this ratio. It is speculated that Mg⁺⁺ would influence the excitability control action of Ca⁺⁺.