Kato T, Saito M, Kondo A
Department of Urology, Nagoya University School of Medicine, Japan.
Urol Int. 1995;54(4):204-7. doi: 10.1159/000282724.
Contraction of smooth muscle including detrusor is initiated by an increase in the concentration of intracellular free calcium ions. Magnesium affects the translocation of calcium ions through the smooth muscle cell membrane. The effect of magnesium ions on detrusor contraction was investigated in vitro using the rat detrusor muscle. Detrusor contractility caused by intramural nerve stimulation increased in a magnesium-free solution but decreased in a high-magnesium solution (MgCl2 5 mM). Cumulative addition of MgCl2 suppressed the detrusor response induced by field stimulation dose-dependently, and 30 mM MgCl2 completely eliminated it. Mg ion also suppressed atropine-resistant detrusor contraction in a dose-dependent manner. After blocking nerve-mediated detrusor contractility with tetrodotoxin, Mg ions inhibited spontaneous detrusor contractions and reduced tonus of the muscle strips. Mg ions suppressed the detrusor contraction induced by carbachol and potassium. The effect of Mg ions on detrusor contraction was enhanced by verapamil but inhibited by Bay-K8644. These results suggest that Mg ions suppress detrusor muscle contractility through an inhibitory mechanism acting on calcium channels in the smooth muscle cell membrane.
包括逼尿肌在内的平滑肌收缩是由细胞内游离钙离子浓度增加引发的。镁离子会影响钙离子通过平滑肌细胞膜的转运。本研究使用大鼠逼尿肌在体外探究了镁离子对逼尿肌收缩的影响。在无镁溶液中，壁内神经刺激引起的逼尿肌收缩力增强，而在高镁溶液（氯化镁5 mM）中则减弱。累积添加氯化镁可剂量依赖性地抑制电场刺激诱导的逼尿肌反应，30 mM氯化镁可完全消除该反应。镁离子还以剂量依赖性方式抑制抗阿托品的逼尿肌收缩。用河豚毒素阻断神经介导的逼尿肌收缩力后，镁离子抑制了逼尿肌的自发收缩并降低了肌条的张力。镁离子抑制了卡巴胆碱和钾诱导的逼尿肌收缩。维拉帕米可增强镁离子对逼尿肌收缩的作用，而Bay-K8644则抑制该作用。这些结果表明，镁离子通过作用于平滑肌细胞膜钙通道的抑制机制来抑制逼尿肌收缩力。
